It feels plasticy, you hear the hammer keys a bit, the display is meager and the ampliefier is a little noisy. BUT...
For under 400.- Euro's I got a hammer action stage piano with a ton of useful keyboard functions, MIDI in and out, and as a bonus a nice sustain pedal included.
It was bought for studio recordings, as a VST controller to play my synths and as a music production/songwrite station.
I did not have any expectations. After unpacking and installing it in the sold separately stand, There was the pleasant surprise of a good piano sound. I would rate it 6 out of 10, since it still sounds a bit artificial. Also there is a tiny bit of artifacts in the reverb and chorus audible. The amplifier, when outputed into the mixer board, has a bit of hiss to it.
Building quality, its heavy and feels sturdy enough. I'd say it could survive some abuse to some degree. On the top is a large monochrome LCD display that does the job, but is ugly. There is lots of buttons, but we miss a numeric pad for choosing the sound from the bank. :( (get this right Thomann!) It would have costed a fraction more and I would have loved to pay for it. Now I have to scroll through dozens of sounds to choose my favorites.
On the back we see a myriad of ins and outs for midi, sound, headphone, power, sustain etc. There is a USB slot on the top but I have not tried it.
When I played the keys, they felt nice and solid, the feel is like a combination of a lot of plastic with a touch of ivory. (no offense you elephants) Just nice enough for all kinds of use from classic to jazz and pop. I would not recommend it to players who play lots of 32 and 64th notes at razor high speed. The springs are a bit slower than with a real piano. The hammers do feel almost like with a piano. I cant imagine how they did this at this price range. When I insert a Grand Concierto VST in my DAW, I do feel like I play a real piano. The keys are NOT wobbly at all.
Build in sounds are good, not great, but there is a very large sound bank with something in their for everyone of your tastes. The strings are only a step down from a Roland JV. There is some realy convincing sounds in there. A pity the reverb and chorus have a tiny aftereffect present in them. Almost as if you here people talking. Its so very soft, but present. Most people probably wont notice it. The drum sounds are very convincing and they are just abundant. It is a great instrument for practicxing piano, drumming, and compose music on. The rhythmic section is pretty extensive so you can have a small band accompany you, including drums a bass and chords. There is a finger chord setting. Lots of accompany styles, more than you would expect. You have all common keyboard options and even can record yourself.
To conclude: sounds are good, play ability apart from some mild hammer noise is great. Build quality it okay, but I doubt if usage on the road would work, it might. The plastic of the case does not feel like it could crack but it does feel very cheap. There is just a ton of options and that is very welcome to the modern music maker. However the lack of a numpad... Come on Thomann, how much does twelf rubber pad buttons cost? And the slight aftereffect sound that is trailing the notes of some sounds is another point to improve and make the SP-5600 an even better budget option. With all the in's and out's, the huge soundbank and tons of options and settings, you get a complete package. For 69.- euro;s extra I can recommend the stand with the integrated 3 pedals. It adds so much to the piano experience.
If you are a beginner with a limited budget under 450.- , you probably want to start with this, you just can not go wrong. If you only need limited functions and a better piano sound, there is Yamaha, Korg and Casio and Roland in the 500.- + price range. Unless you prefer to save up for something of more quality. If you have a higher budget, the sound and build quality as well as the options, will just not be of high enough quality for the more demanding players. Very good sounds come with a very good price tag, but I think that is not what the SP-5600 was build for. It is very good at delivering all the options one needs, in an affordable package. I look forward to an improved 5700 with a num pad and with improved sound quality that has no aftereffects and a bit lower noise in the amplifier.