Yeah, I used it, it's a nice compact application, doesn't take up much space.
Only problems were name issues for MSN (Basically, all other MSN clients would update the display name when I changed it, except for Fire), and it unblocked everyone on my contact list.
I've used it earlier .. then tested Proteus (as Fire seemed RAM consuming in the days of 10.1 and 10.2 ..) ... and then Adium. Fire isn't bad, but as all 3 multi messengers are nice, maybe test all of them to see which one you like most?