Hi Mira,
Yes this offer is risk-free and you treat it as SnR bet. (stake not returned)
Set your calculator to SnR when placing this bet and look for high odds horse race.
If your bet wins, you are done with this offer.
If it loses, you get $25 bonus bet to be used on any race.
Yes- you need to back and lay with Betfair.
If you still confused, read type 3 bet below:
https://matchedbetting.wpengine.com/horse-racing-guide/
Cheers