i emailed them for more info and this was the response:

FLEX will work with our trainer and also on the road. The power output formula is proprietary and we can't give much detail, but it is accurate!

Regards,
Minoura Technical Support
PH: 510-538-8599
FX: 510-538-5899
support@minourausa.com
www.minoura.jp

translation: just buy it and trust us it works