go and listen to them if you can. i too think the alesis m1's blow the behringer truths away. i wont comment on the 824's, because i dont like them for mixing.
a lot of nearfields are shy in the bass area, which isn't a problem. but if you want the extra response, m1's have a lot of bass in them.
i would definitely get them over the truths, but have a look round and see what else is in your budget before you buy.