From my experience I find any of the trusted vendors advertising on this site provide a greater service model than just price point. I've been building quads, hex's and hopefully soon an X8, for 5 years now and wouldn't put anything from Banggood, Aliexpress or Bestgear onto one of them. For my money, and yes it can be considerable, I prefer what I consider quality goods that give me a better sense of assurance for the type of flying I do. I'm not totally against the cheaper vendors but I also weigh the use of the rig I'm building into the equation. If it is something that is meant for training of fun flying I consider the cheaper alternatives but if it is going to carry a couple thousand dollars worth of camera, lens and gimbal around I'll gladly pay the price for peace of mind and quality service I get from a professional parts provider.
Some of my friends over on FPVLAB are always testing the bargain goods from the vendors you mention and for them it is perfect since they are mostly flying cheaper foam wings and planes meant for long distance flight and even the occasional crash from intense FPV flying, they can easily be taped up and flown again with little or no expense. If that is all your planning on doing is fun flying than by all means go the bargain route, it will provide you with the gear you need to enjoy and grow in this sport/hobby/industry for years, BUT, if you plan to pursue a career in this technology sooner or later you'll learn that you get what you pay for.
I can tell you that spending $500 on a gimbal that supposedly is the next best thing compared to a unit the costs $2500 and is a proven winner can get costly when you figure all the extra time you spend troubleshooting and tinkering on the cheaper unit so in the end it may have been cheaper to buy the better unit in the first place. But, if you're still learning to fly a bigger rig, than a crash with a cheap gimbal is better than trashing an expensive one.
Many of the members here do this for a living and most are very resourceful, full of knowledge from years of flying and building RC planes and helicopters before the quad or mulitorotor was introduced to the masses, and are willing to share their experience with anyone new or old to the community.
IMO buy from where ever you are comfortable but just because a place sends you a replacement for free doesn't mean that they fixed the problem or that the new one will work any better. Sometimes you end up spending more in the long run buying cheaper parts only to find there's a reason they are cheaper and don't always work as advertised but that all depends on your personal use and goals of your equipment.
Either way, enjoy and fly safe...
