With the M71 you can give the channels silly immature names (so ch69 is "Your Favourite Channel", ch71 up here becomes "The Voice of God" etc). Hold on, you want sensible advice?
Our M71s were used in a commercial enviroment, 6 of them (and another 8 at a different centre). Overall, we like them, a lot more than the M31s or even the M90es (the hard as nails commercial ones that are now dying slowly).
The M71 aerial has proved pretty nasty in continuous use with us, all of ours are wrecked by now (and no one's admitted to chewing them or anything). On the plus side, they are pretty small and ergonomic, the units themselves are well enough built, the belt clip is sensible (unlike the M31s - which is a joke), the aqua quake water draining thing works, and the HM-125 speaker mic is rather nice (if looked after!).
That aerial really sucks though. If you were going to get one of these units, then try and fit an alternative.
Now off to the boatshow for me, I got £300 to spend and new VHF
Oh yes, the M71 definately doesn't float. But I say use the wrist strap to secure it, and get the fist mic. Its luverly it is