If there is indeed fent in them you want to be very careful, but I suggest not doing them at all. If it is something "rare" and they are going around have it sent off somewhere to find out exactly what is in them.
I've snorted fent, just a tiny tiny (like 1/6th of a match head sized bead) of the gel from one of the patches. I mixed it with some power from a perc 10 I had laying around. Cut that into four small lines, and split them with a friend. Made sure to work the powder around for like 10 minutes just to make sure it was mixed as well as possible. Also, at the time my friend and I could both handle 60mg of Oxycodone (as in, that's what we were doing to catch an alright nod).
Anyway, that shit scared the hell out of me, I was shaking. My friend went outside, I figured he was throwing up because I felt like I had to as well (didn't though). I went out to check on him and he was out there blowing his nose as hard as he could attempting to blow that shit out and we're talking about a guy that'll do almost anything not to waste a high.
So my point is, don't mess around with fent, but if you do be very careful about it. Its too hard to measure out that stuff effectively for your average pill head.
I wouldn't trust these man, for all you know they could just be bunk pills too. Even if you trust a source you have to realize he might get scammed too from time to time and sell you something bad without knowing it.
Again, I would not take these until you've had a bit of one tested to see exactly what's in it.