...You can usually get a good idea about the quality and reliability of very specific modules over on the MuffWiggler forum. I don't really think there are inherently good or bad manufacturers or modules.
...
I do tend to shy away from DIY modules that other individuals have built, probably unjustly. The clones I have gotten from After Later have been great, but I'm not sure I trust DIY from a random individual.
-- farkas
Yes to all of this.
I bought a few DIY modules that were faulty, in a non-obvious way. In most such cases I didn't research enough to have a clear idea of what to expect. There are a few respected builders here who deliver premium build quality. such as RTFM. No problem ever. On the other hand I bought a module from Russia that really looks home-made, rough and raw alu front plate with handwriting on it. And it, too, performs flawlessly since the day I got it.
Most problems I had came from a lack of research or bad judgement on my side.
Make sure to have buyer's protection if you are not sure if you trust a seller, DIY or not.