Yeah used break in fuel on a Mito 4 and a Roma .25
The Mito went great for about 4 to 5 gallons, but has massive crank pin/rod bushing wear which caused the rod to crack, this happened right about the time it started to not hold a tune. I discovered that right on about 3 laps it would heat soak and then lose all compression.
The Roma went bad after 3 maybe 4 gallons. Same story cant hold a tune and loses power/compression when hot. I would only use break in fuel for an emergency /big event type situation