The Yamaha NP-11 Piaggero Portable Digital Piano is a fine example of a low-budget, beginner to advanced player digital piano.
I recently sold a Korg SP250, which by rights is a proper digital piano (in that it has properly weighted keys, is the full width and weighs a tonne). The Yamaha NP-11, which rocks in at £350 cheaper than the Korg impressed on opening!
It lives up to its reputation in many ways. Much like the Korg, the NP-11 has a realistic grand piano voice, which you would expect for a company with such a historical share of the piano market. I wanted something portable but still piano-like for taking to gigs. The NP-11 has piano-style keys, about half weighted but the correct size. I enjoy the weighting of piano keys over, say, a keyboard, but with full-weight keys comes a heavy piano! The NP-11 weighs around 5kg! You can lift it with one finger. Compared to the Korg (which was about 20kg, this is definitely a 'portable' digital piano.
What is great about the NP-11 is despite being comparatively cheap to other electronic pianos, the quality is still there. It sounds great, feels great to play and even looks fancy, even if it is all plastic.
Due to the weighting of the keys the keyboard is suitable for beginners, especially children. Although it is not a full size piano keyboard, there are enough octaves there to play a wealth of songs. Unless your training to be the next Beethoven you should be fine.
Hidden in the keyboards disappointingly vague control panel are a number of additional tweaks that can be performed to the piano to alter its sounds/effects. Aside from having a small number of voices (which is fine if the intention is to use it as a 'piano'), you can alter the reverberation, octave, touch sensitivity, tuning (and transposition), amongst other things.
The only downside I have found with the keyboard is the control panel being so vague. I personally stuck a bit of masking tape on mine and wrote down the short cuts, but this is to help me when I am playing at a gig and want fast control. In time you will remember how to alter them all without the booklet (which is very clear). For general day to day playing, the piano is great. I prefer it to my £600 Korg in many ways and am glad I made the change.