Well, I did some websurfing for the specs of your chosen unit. For the projects you're talking about it should work ok, but here's a list of pros followed by cons:
Pros

Ease of operation. You can probably start using this right away.
A fader for each track. This is very helpful if you want to mixdown your masterpiece to regular stereo cassette.
Cons

Ordinarily, you'd mic a piano with two microphones. Only one track can be recorded on the x-12 at a time. Since you're going to record an acoustic piano, you'll have to mic the sweetspot and hope for the best or get an outboard mixer (cheap yet quiet ones ARE out there) and get a good ambient mix to send to a single track. The only way to record the piano in such a way that you can pan in the mix, you'd have to mic each side of the piano for two seperate passes. Each pass would have to be exactly the same too, so the practicality is just about nil.
There appears to be no effect sends on the unit. If you plan on using any sweetening on the vocals, you'll have to shred them wet. Otherwise, you'll have to add effects to the whole mix (which shouldn't sound TOO bad) or each channel would get it's own effect (which would sound icky). There are other work arounds, but to use them means to make good arguments for shelling out another 50 or so dollars for a unit that has the above.

To Sum Up.
If it were me, I'd put more money into it. $199 would probably get me a fine portable to accomplish what you want to do. If the budget is set in stone, then go ahead and buy it (it looks like a fun little toy) and buy yourself a tiny mixer (Rolls makes some as does MidiMan) so you can record the full spectrum of the piano and maybe even get better control of the effects per instrument/vocal.
Good Luck.