If this is a product you really want to use, then the only 2 things that matter are bloodwork and gains. If the product makes you stronger/bigger, and bloodwork looks good while you're on it, it's a good product. You've already used PH's, so there's no reason for me to try to convince you not to do them in general.
As far as conversion rate goes, and the stability of the product in general, whether it actually converts to Trenavar or anything useful in the body,it's really anyone's guess as to what's actually going on. I've never seen data on the product, and I don't expect to. This MAY be an effective product, but I've never seen anyone on the boards here talking about it. Looks like it's only available in Europe, so that may be part of the reason.
If you really want to know if it works, use it by itself. That's the only way you'll be able to tell.