clen may or may not have extremely bad side effects. Possibly life threatening. I have yet to see this proven in Humans but the possibility is there. Taking clen is a risk.
Clen has never been shown to be anabolic or anti catabolic in any human studies but it has in animals. It is "Brologic" that has given clen its anticatabolic tag. Many users feel it helps retain muscle gain. I have never used it on its own in PCT so i could not say what helped me maintain muscle. I would say that diet and training are more important in retaining muscle than any drug.
I will not be using clen anymore as I feel there are safer options available.

For fatloss - DIET! CARDIO! ECA,Albuterol.
Fight catabolism in PCT - DIET! TRAINING! Agressive PCT,Slin,IGF,GH,MGF. possibly try myogenx supp too.