If you only have one flight planned for the trial period, I wouldn't do it. You're liable to spend as much time enrolling and getting it set up than you will save by using it, maybe more depending on the airport you're flying out of. CLEAR can be much faster at some airports and in some situations, it can also be slower. I had it last year for about 6 months, used it on roughly 10 flights and I think it saved me a grand total of 4 minutes, all of that was at MCO. It cost me time at ATL, ORD, DCA and MKE.
There is no difference once you get to the screening line. CLEAR brings you past the document checker and puts you in whatever line you belong in at that point.