There are a lot of mixed feelings about M-Audio's digital pianos. One thing I've seen come up often is "quality control". I've seen reviews compare M-Audio's quality control to that of Alesis--which can be quite iffy at times.
I played this model a few weeks ago when demoing other boards. It wasn't bad really. The action is a semi-weighted keybed, and it felt decent enough for some expressive playing. The build quality IMO isn't the worst, but clearly not the best--again this unit is under $400 so I would say the build quality matches the price.
The piano sounds were better than I expected to be honest. You're not going to win any piano shot outs with it, but the piano sounds would get the job done. The other sounds weren't too bad either. Again, they would favor well in a mix.
The thing with this model is if you take it for what it is then I think you'd be happy.. As long as you didn't expect too much from it. In all it's a 17lb digital piano with semi-weighted keys decent sound, and 126 note poly.
This unit would also make a nice midi controller as well. Personally I'd look at it as more of a good midi controller with an added bonus (being the sounds).
**one thing to at least check on for sure..., there have been complaints about M-Audio's velocity switching settings between the layers of their sounds. Some have said it's not consistent, others have not. Personally I didn't notice any problems with it. I do know the models bellow this one (silver semi-weighted midi controllers), have had MANY complaints about build guality, failing keys, inaccurate velocity across the entire keybed, and more.
Squeak
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.