To follow up ALL the posts on suspension I have made recently...
If you notice I have not made any suggestions for off the shelf coilovers. That's because I can not say any are really good dampers. The only off the shelf coilovers I would recommend would be JIC FLT-A2 and tanabe sustec pro-7 (for s-chassis Stance is by far best bang for the buck). And coincidentally these are the dampers I have the least personal experience with, I just know a lot of experienced people that tell me they are good (not just internet hearsay). If you want a good suspension, you have to pay up. Just like you wouldn't throw a junkyard turbo and expect stellar results.
That being said. If all you want is less body roll, a lowered stance, and generally better handling, these off the shelf units are not too shabby. Than the only thing I would be concerned with is how long they last, price, and most importantly customer service. How easy/cheap is it to get replacement dampers if yours do blow?
I have a team mate that runs the megan coils on the s-chassis...and actually a lot of drifters do. The ride is shit, and if they wanted better overall grip they would go elsewhere...but in drifting it's not all that important and the things are well made, it's just the R&D to properly valve the dampers is not done.