No big heat issues. Just small fans blowing air up on the lights. If buds get too close (say 6") there can be a bit of stress. Have to watch your leaves. I have plants tied back and such. Cooltube was no different and the actual ambient temp of the grow increased with the cooltube so I figured why filter out any light with it, especially if the temps didn't decrease. I ended up giving away the cooltube.
There could be some applications (like CO2) where cooltubes might be a wise investment.
Next round I am probably going to build a cage to scrog a bit better with, but the plants I have actually found are going reasonably. Could do better but I wanted to see how these plants would grow.