Letro seems to be a pretty effective AI. I have spent long times on it with little problems. As to sex drive it is normal for it to be up and down, test alone does not regulate this, it is a very complex bunch of factors at play.
I have found the combo of tren, deca and test of course to be too much for pretty much anything though, had me getting gynoy even on 1.75 mg letro ED
When getting in shape for comps I will go up to 2-3mg ED