None of the original research I've read on the constituent herbs in HCGenerate (Fadogia, Fenugreek, Tribulus) tested the effectiveness of continuous usage against intermittent usage, so the only answers to your question I think you could expect are anecdotal.
Having said that, I suspect that any exogenous herb or drug that provokes an increase in LH is gonna provide diminishing returns if used continuously. Just a guess of course, but the few things I've used to boost LH (and thereby T production) seems to drop off a bit in effectiveness after a while.