Opinion on friends with benefits?

I have this guy friend that we've been friends with for ages. We have such a high level of trust which I've never had in any relationship before, not even my ex of a year and a half. Conversations have started to get flirty and I dropped the bomb of friends with benefits as a sly joke but he thought it'd be fun. We don't want anything more as we're both getting over long-term relationships (me a year and a half and him two years). What are your opinions on FWB?