I don't know how much experience you have with keyboards, but the idea of 'weighting' varies from manufacturer to manufacturer. I have an Ozone, actually. It's handy really only for the audio interface -- it captures audio off a good microphone better than any USB product I have come across, but that's more or less a function of the microphone.
Key weighting on this device is similar to any cheap weighted keyboard, similar to a Roland 4 octave or 5 octave synth, it's not hammer-weighted like a piano or to simulate any physical response. It simply provides higher resistance at the bottom of the stroke than the top. It's designed to make it easier for you to attack the key the way you want over something with no resistance. If you aren't experienced with keyboards or a piano, putting the proper expression into the music you wish to achieve, but if you have been around these type of instruments, both M-Audio's and Edirol's inexpensive USB keyboards will serve you well. Actually, checking the website, I saw that they have a similarly priced model called the Axiom 25 -- the trigger pads are a pretty sweet feature, I've enjoyed using them on other gear in the past.
I don't find the knobs useful at all. I prefer to control what I need on the screen, actually, if I'm using a desktop keyboard. Once you learn the controls, setting octaves and offsets and such is very fast, and you'll need to do that a lot on a 2 octave keyboard. For the occasional foray into techno or whatever loopy stuff you may be into, this is just fine, really, you'll be working very quickly.
If you actually want to build some chops, and you're going to be facing away from the computer because you're concentrating on a larger keyboard you can use 2 hands on, consider a 49 or 61 key model.
I can't say if the weighting is significantly different between different M-Audio models.
