The trick to using clen is to start VERY slowly. If you go to fast you will NOT build any muscle. You will not be able to workout properly if you feel like shit. Also, you shouldn't take clen immediately before your workout, ingest most of it 2-4 hours before
I put on 3lbs of LBM my first 2weeks of clen and da big thinker added .25inches on his already large arms(on 1800cals!!!)
He followed my advise and started slow.
Clen does not build muscle per se like AS. It helps you (tremendously) build muscle.
People don't realise how potent it is for workout recovery. That's its strong point, you should be overtraining on Clen.
I trained my arms 5times in a two week period and gained close to half an inch on my arms (as well as 2lbs of lbm) while eating a grand total of 2500cals.
So yes, Clen is awesome if used properly. The only problem is that your body gets use to clen very easily