Everyone seems to agree that, having been made at Izmash, what was actually made at Izmash will be 100% top notch. Since a lost of stuff had to be replaced to comply with 922r, and they don't import them the way you see it in that ad, there is much question as to how much Izmash is left and how well it all was done.
In general the crucial parts are the barrel, bolt, carrier, receiver, trunion, and rivets holding those together. Those all stay the same on nearly all conversions.
Trigger groups are usually replaced. TAPCO and K-Var both have perfectly functional US-made trigger groups.
Furniture is usually replaced. You have to work hard to make furniture so bad that it causes reliability problems. TAPCO, K-Var, and Ironwood (for wood) are the most common options it seems. All are fine. In my personal experience the K-Var furniture doesn't seem any better than the TAPCO furniture, and TAPCO is usually cheaper. Ironwood makes terrific wood if you want wood.