This looks like it might be an old add.........here's the first paragraph from the tech notes:
"
O.S. has Updated the .25 SF with this New High-Performance .25 FX.
This Engine may be used in Sport and Aerobatic Aircraft. The FX is Designed to
Use a Muffler or Tuned Pipe. Comes with a 2-Year Warranty."

The 25 SF has been MIA for many years............

DON'T GET YOUR HOPES UP!!!!![]