Should I use capillus laser cap if i am going for another hair transplant in 6 months time?

The Capillus definitely works works I would say that the results per dollar aren't necessarily worth it. My personal suggestion would be do a series of PRP treatments and then the transplant. Nothing is better than a transplant...yet. 

I think it will help get you ready for the transplant. Revitalizes the tissue and helps in regeneration.

The use of a laser cap will not significantly benefit you for growing hair and the cost of this product is very high

Worry not. There is little evidence that laser light therapy can grow anything that the average patient would call hair... let alone anything that could be extracted and moved to the front.
FDA cleared simply means that the FDA did not find any risk of harm and there are no other available treatments so we might as well let people try it. Much like propecia which still sells hundreds of millions and at the most may give some photographic fuzz in the crown area!!
Basically what is being sold at retail is a cap with some red lights inside. Nice mark-up if you can get it!!