Ballistically it's pretty darn close to 22mag - with a 30gr bullet the 5.7 is something like 100fps faster. But it's got centrefire reliability, it's reloadable, and it's got panache.
If I had more money I would have bought a Ruger 57 in the last few months, at which point buying this would be a no brainer...
Edit - its more like 500fps difference. See post 17 for context.