They do fit the guide rail. The clamps don't fit into the MFT holes, however, because the corner of the L isn't rounded like a Festool clamp; it butts to a T. Otherwise, I like the clamps for the rail since they are faster to use than the Festool clamps. As I posted in another thread last night, the T-square attachment can be snugged for zero-play and mine at least is pretty much dead on (not measured with a square; measured measuring the sides and hypotenuse, which is better for a 24" crosscut). I do not have the miter attachment, though it attaches the same way and should be similarly useful; don't know if it slips a lot like the Festool is reported to do (don't have one).
If you wanted to dedicate a guide to crosscuts, you could certainly get the T-square to be dead on. It is machined out of one piece (or cast; dunno) so there are no attachments that can work loose later.
Only $30 for the T-square. Can't recall the clamp price.