The M300 is dirt cheap! I picked it up off eBay for around $250 AUD incl. shipping....brand new, in the box, and probably saved at least $300
I cant compare it to the waves bundle, having never tried it.
It is a largely preset based FX unit, although it does have some control over decay, pre delay, and 'colour'. Also, the main benefit is that it will not eat up your CPU, as most plugin based reverbs are very processor hungry. Also, having S/PDIF I/O means I can send a signal digitally to the M300, and then digitally back, so there is no AD/DA stage. Very cool. It takes its reverb algorithyms from the high-end TC Electronics reverb engines, and they are nice. And then it also includes some other FX/compression/de-esser etc
If you have a fast and capable computer, then the plugin reverbs are just as good, if not better. And if you have something like the
Powercore compact, or UAD-1, then you would definately be better off with this rather than the M300
Personally, I quite like having outboard gear. And it goes well when I mix through my old analogue console.....