I've used a couple Freaks with my SP-1. Both borrowed until the local shop gets more Freaks in.
I'ver looked at other barrels, like the J&J, Stiffi, Deathstix, Python and have decided for me the Freak is the way to go.
I almost bought the Deathstix, due to the reverse thread between the sizer/back and the front, the sizer can't get stuck in the breach/shroud. The Stiffi has a short sizer and am concerned about the front seperating from the back upon attempted barrel removal.
A friend of mine bought the J&J for his SP-1 and seems to like it.
The Python I have the same concern about the back staying in the breach/shroud when removing the barrel. There are also only 5 sizers available.
The Freak also has the most available inserts/sizers I've seen, at a pretty inexpensive price, I could also make custom sizers on my Grandfather's lathe if I feel the need to.
If I ever change markers or buy another one that doesn't share the same thread I only need to buy one back, not another complete kit.