Not all replicas are poor quality products, but you have to choose carefully and be well informed of who makes the wheel.
Even OEM AMG wheels are not made by AMG per say, they commision Italian wheel makers like Cromodora, Rondell etc to produce the rims. And such companies also make plenty of 'style' rims for the replica markets.
There are some really shabby reps out there, but if you choose carefully, there are some real bargains to be had. However, if you're not sure, or if the supplier cannot tell you who made the wheels, then you'll be better off sticking with the 'selected' 'OEM' wheels.
I had a set of BBS styled alloys made by Velocity Motoring on my M3. They are some of the best wheels I've ever used, and at £100 per wheel, I didn't even bother refurbing the kerb ones. Just replace them with new!