I have this AM15 upper. I also had an American 180 as one of my first machineguns. Pros, the AM15 upper is a heck of a lot cheaper than an American 180 now (although I think I only paid 2400 for American 180 long ago, and years later traded it for the M16 that the AM15 upper is on now lol) but on the downside, I can only reliably run it on CCI minimag cprn rounds. Still, the M16 that the AM15 is on had a Spikes upper on it for years, so no worrying about changing the fcg out, as it will stay AM15 dedicated. It is loads of fun and I would recommend it to anyone. It is the American 180 experience without the cost. I would not recommend it if you are going to caliber change often. Just put it on your other M16 The rate of fire and the design is appealing with this AM15 upper.
If you dont want to go AM15 route, I have heard the CMMG kits are good but you're not going to get the longgg drum dumps this way.