I find the Tapco stuff I've tried is very serviceable, although as mentioned the AK side folder is terrible and an obvious exception. If you actually look at one before buying, the Tapco AK side folder is obviously crap, I don't understand why anyone would ever buy them.
I never tried their AR or AK mags, but I've had 100% function with their Galil mags in my converted Saiga (I've a half dozen of them).
I'm very happy with the price/performance of their M4 style AR stock, although I think the DPMS one at about the same price is a bit better, but the Tapco is much easier to find. I don't think too much of their AK M4-style stock -- I much prefer the ~$15 UTG AK to AR stock adapter and the Tapco M4 style AR stock (I end up with a spare buffer and spring)
Their single & double hook AK triggers gives a better pull than any of the comblock triggers on imported guns, I'm slowly replacing them all in my old Maddi, Romanian, and Chinese AKs.
Their customer support is pretty good, I had the sling mount / clamp screw on my Galil style AK handguard break, sent them an Email asking how much a replacement was, and they just sent me one for free, no questions asked.