Foot retention is a good thing in any kind of cycling, and even more so with FG. You can find pictures of some pretty knarly injuries from pedal on shin action due to runaway pedals on a FG. Puncture holes and ripped up skin and such. But beyond the safety issue, developing good spin is important for efficient one-gear riding, and foot retention tends to improve pedaling technique. Amirite?

So I recommend finding a foot retention system that works for you. Have you considered Powergrips?