Clen is crap. I had these dreams of using clen while working out hard to do the same thing you are talking about. Yes it was legit and no I did not like it. I noticed that at higher dosages I was cramping like mad after hard workouts. I had no wind and I was not noticing the results I was wanting to see.
Granted it may have been specific to me but my advice would be to avoid the clen and stick with a good clean diet and just resist the urge to eat the bad stuff when you are putting on size. Stay smart and the BF increase will be minimal. If it is put on with quality foods then it shouls come off easily as well.
Just my advice. I don't like Clen at all though. Stuff is horrible. Horrible, horrible, horrible.
Late,
Gig