I have the Roland FP-30, not the FP-30X. However, the pianos are almost identical. The only differences are related to software aspects such as polyphony, Bluetooth, and overall synth sounds. The speakers, keys, key action, and recorded piano sounds are the same between the two models. Since the FP-30 is no longer available, but the pianos are practically the same, I will copy my review for the FP-30 here:

For its price (700€), it is truly the best. I tried it in person at a well-known store in Germany that has a huge variety, and it surpassed anything up to 900-1000€.

The piano sound is of a good quality. It is certainly not perfect, and sometimes it can sound a bit harsh in the middle to high octaves (around C5-C6, especially if you play the keys too forcefully). Generally, you need to adjust your playing and learn to strike the keys softly if you want to produce a sound that is not sharp. Without having much experience playing on classical pianos, I like the feel of the keys and I can play with the sensitivity I want, having good control over dynamics.

It has three piano sounds, but in my opinion, only the first one is worth it, as the other two are more treble-focused, and it already doesn't have much room to enhance the trebles. (edit after experimenting: the second piano sound is very pleasant when playing with headphones. It has more reverb and stereo elements, it is sweeter, and I think it fits well in pieces like Chopin's nocturnes). Additionally, it has electric piano sounds, harpsichord, church organ, strings, and various other similar things. The truth is that they are not something extraordinary and you shouldn't pay much attention to them. They can be fun to experiment with if you want to try something different in a piece, maybe even useful in a live performance, but if you plan to focus on such things, it's better to go for a synthesizer or something more suitable for that kind of work from the start.

You can adjust various things like reverb, brilliance, key weight, etc., but I didn't find that they improve the sound, whether I tried increasing or decreasing a setting. Generally, the default settings have everything at a moderate level, and I think that's the best choice. Perhaps the key weight may be useful for someone. You can adjust the keys to require more force to produce sound, giving you the simulation of playing on a piano with heavier keys. Of course, you can also make them lighter or even disable the sensitivity completely and play at a constant 100% velocity.

The pedal it comes with is not good, so consider getting another one for 10-20€. The truth is, I haven't replaced mine yet, even though it doesn't suit me at all.

It has two outputs, a 6.3mm jack and a 3.5mm mini jack. Both are stereo and you can connect headphones or a cable to connect to a mixer or sound card. The default setting is to mute the speakers when you connect a cable, but you can activate the speakers by pressing Function+F#7 (Function+F7 mutes them again). The sound from the outputs is quite sharp, but it is at a level that can be comfortably used even in live performances.

Overall, I would say it is an excellent choice for an affordable piano. I wouldn't go for anything cheaper than this, and to justify something more expensive, you would probably need a budget of around 1500€.

I have had it for a week now and I am completely satisfied! Apart from the keyboard, the stand, the chair, and the headphones that the bundle offers are excellent. The chair is very comfortable and the stand is sturdy, as for the headphones, their sound is quite satisfactory. The only problem I have is that I haven't been able to find the right height combination for the chair and the stand.

As for the keyboard, it is amazing! I used to play on a Yamaha U3 classical piano and I didn't believe that a digital piano would have such a good feel. I was wrong. The FP-30 has weighted keys (maybe even more than it should) and high sensitivity to touch, simulating the feel of a classical piano very well. Its construction is durable and beautiful.

I highly recommend it.