One of the things you notice in this hobby is the cost difference between traditional RC companies like Blade and Walkera and the companies that started out making toys and moved to remote control toys, like WLToys and SanHuan. The explanation for this is usually that the former are Hobby Grade and the latter are Toy Grade. I'm going to illustrate the difference.
Over the years, I've bought 11 different blade 'copters (an MCX S300, MCX2, MCX Tandem, CX3 MD520N, MSR, MSRX, MQX, NanoQX, 350QX, 200QX, and a 200SRX). I've also purchased a Walkera Mini-CP and a Nine Eagles Solo Pro 126v2 Night Edition. One of the Blades, the Walkera and the Nine Eagles came with controllers.
In addition, I've purchased a DX6i and DX5e controllers to use with the others. I've also purchased 2 Walkera controllers.
Every one of the aircraft flew out of the box. Maybe not well, and maybe not quite as designed, but they were at least flyable. Only one of them was in any way broken. All of the controllers worked fine for flying out of the box, though one of the Walkera controllers had a broken USB port causing me to exchange it.
The MSRX had a nasty design issue in that anything more than a little rudder input tended to cause it to start flying off to one side or the other. This made it a PITA to fly, so I sold it. But it was working as designed.
The first 200SRX flew fine - except that it didn't self-level in intermediate mode. I exchanged it, so it gets counted once.
Any problems that I've had with Blade products after the fact - mostly meaning things breaking long after I bought them, or replacement parts that turned out to be broken in some way - were generally fixed with a call to Horizon, and a replacement was in the mail to me that day or the next. Lately, they aren't doing as well - they can't seem to decide how their new products are supposed to work.
I haven't had a chance to check Walkera or Nine Eagles customer support, but reports are they aren't as good as Blade.
All of them have been relatively durable. Further, when they do break, replacement parts are readily available, and repair is usually relatively simple. They are designed to be repaired when broken.
My experience with WLToys isn't quite so extensive. You'll see why shortly. But I've bought 6 of those: (two V911s, two V939s, a V959 and a V915). I purchased a second V911 and V939 to use for spare parts. All but one of these came with a controller.
Of those, four were broken in ways that made them unflyable when they arrived. Three of the broken ones had broken controllers: one didn't power on, one didn't transmit, and one suffered from intermittent power loss. Flying with the last one just isn't an option. One 'copter didn't power on and one copter was the wrong version so I didn't have batteries (not the manufacturers fault).
The V915 was the worst case: it came with a controller with an intermittent power loss, and a broken LED on the helicopter. The latter doesn't make it unflyable, but it's still not working properly.
The companies that sell these - at least with the price difference pointed out earlier - have customer service on the other side of the Pacific, if not shipping from there. While I've written about these experiences at length, the short version is that it usually takes days to sort things out, and involves at least one exchange to clarify things for someone who speaks English as a second language.
The 'copters themselves seem to be about as robust as the hobby grade ones. The difference is, once you've broken them, repairing them can be a lot harder. Parts may not be available, and doing the repair is probably a lot more painful - because these are designed to be broken and thrown away. Some are cheap enough that that's not unreasonable, but that's not the case with all of them.
The controller is very important, though until you've flown with a reasonable hobby-grade controller - even a relatively inexpensive one - you may not realize this.
All of the controllers but the RTF Blade controller and the DX5e are computerized controllers. They have the ability to store multiple aircraft configurations and correct aircraft flight issues in the controller. They all have or can be configured to have a throttle hold, which is an important safety feature.
The best of the toy-grade controllers isn't as good as the worst of the hobby-grade controllers. The sticks just feel cheap, the gimbals aren't as smooth, and the controls don't feel as fine. The only hobby-grade controller that felt as bad as the toy-grade ones was the Walkera RTF controller, and installing $3 replacement sticks fixed that.
None of the toy-grade controllers are computerized. There is no throttle hold (though maybe the controller for a collective pitch helicopter would have one) and no way to configure one. There is no way to correct flight characteristics in the controller.
The toy-grade controllers copy the look of the computerized controllers. But that's all it is - the look. This is actually bad. For instance, while the newer ones have a standard five-way navigation button cluster, the five buttons do unrelated things, or are non-functional.
The worst feature of WLToys 'copters as a line is that the protocols seem to change willy-nilly. The six-axis version of the V959 - the V222 - uses a different protocol than the V959. The V912 - a six-axis helicopter - uses the same protocol as the V959. Except that the way they control the FPV camera on the devices is different. So while you can fly the V912 with the V959 controller, you can't control the camera, and other controls may well be mislabeled.
Finally, the worst feature of the controllers as a whole is that they tend to encourage bad habits. The lack of a throttle hold function is one issue. That some of them require turning on the aircraft and then the controller to rebind it every time is another.
Other than testing things, I won't fly with these controllers.
Most of my hobby-grade purchases have not included a controller, since I can use the same computerized controller for all of them. But most of the failures of toy-grade purchases have been the controller. So maybe things aren't so bad.
If you look at just the helicopter failures, it's 1 broken-but-flyable hobby grade helicopter out of 13 and one broken-but-flyable and one broken and unflyable helicopter out of six toy grade ones. That's over twice the failure rate.
And it's one broken-but-flyable hobby grade controller out of five and three broken and unflyable toy grade controllers out of six, or nearly three times the failure rate.
You get what you pay for.
I no longer buy toy-grade rc aircraft, except in unusual conditions. I must have a good reason to believe that I can fly it with a hobby-grade controller. If that isn't there, the sale won't happen. And there must be no comparable hobby-grade aircraft. So far, that means either a really nice scale body, or a multi-rotor configuration that's not generally available in small sizes.