It is far too easy to put a synth engine into a controller these days, especially one with off the shelf sounds that might check off a box from upper management but does nothing for a real musician. In this case, the product actually makes no sound on it own...HOWEVER, there is a companion app that makes the sounds. And is the editor for the device to tell it how it reacts and all the rest of the setup.
So technically there are 'synths' and there are 'controllers' and then all sorts of things in between. Samplers are not considered 'synths' by some...however what is sampling other than practical application of FFT synthesis. And then you have 'romplers' where they are samplers but all the samples are baked into ROM and you can't change these. Again, synthesis but someone glued the knobs shut. And hundreds of more names musicians will call each of these. However, if it makes noise, I call it a synth. In this case, the 'block' is a hardware / software combination and even if you can use solely the hardware for something else...I'd still call it a 'synth'.
In this case, the software app does the synthesis. Its cool, but it doesn't sound 'almost as good as it looks'. Sounds pretty shitty. I know one of the 'keyboard wizards' that did the programming for this product, and he is more known for their soulless playing style that favors speed over style.
That said, yes...as a midi keyboard it is AWESOME. It supports polyphonic bends. Polyphonic aftertouch (I have a synth from the '80s -- EPS16+ that had polyaftertouch and it was amazing...and then no one made anymore for 40 years!). It supports midi OFF values (as opposed to just on...how quickly you lift your fingers actually affects how a real instrument reacts...why should a synth not give the same options). It is very expressive. I played with a solo violin patch that was based around a sampled strad but using granular sampling techniques to allow seemless switching between different articulations...and it was GORGEOUS...but it was also a $500 library that you used on your Mac
At this point, I use MOSTLY software packages and barely anything out of the box on synths. So much easier. I have a few instruments that could go out without a computer -- ones that I programmed pretty much all the sounds I'd use and I'd still prefer to use my laptop or iPad with specialized software. It is just so much easier to program and to get things dialed in.
So hopefully this answers your questions and I'm not just rambling on after midnight...I'll be more coherent in the morning.