Here are my thoughts on the subject. Certainly, if you like the PSS-A50, then buy it as an addition to your set-up. It can make a great "scratch pad" to experiment with composing melodies or creating sounds on the go when you cannot have your Genos with you. And, it could make a good addition to your Genos, where you could mount it above your Genos and play both keyboards together. This would allow you to quickly jump to the PSS-A50 to play a melody with a different tone while playing a song in real time without having to push any buttons on the Genos.
However, I would not recommend it as a keyboard strictly to learn piano technique because it has mini-keys, which means the individual keys of the keyboard are significantly smaller than the standard sized keys on your Genos, a piano, or a synthesizer. So, if you get used to learning on the PSS-A50, then you'll practically have to re-learn what you've learned when you transfer your technique to your Genos or a piano. And of course, for actual piano playing, you want something with weighted keys, but as you want something that is very portable to carry around with you, I realize that might be asking a bit much. However, you might be able to find something that at least has a touch-sensitive keyboard -- meaning that, even though the keys are not weighted in feel, they at least respond with louder/brighter sound when you hit them harder, like a piano would do.
There are a variety of small, lightweight keyboards out there that at least have full sized keys, which would make transferring what you learned to your Genos or a piano much easier. Unfortunately, most Yamaha keyboards with full-sized keys are going to be at least 5 octaves, and therefore quite large to carry around. Yamaha used to sell a variety of beginner "home keyboards" with 4 octaves, which would be more portable, and which you can find on the used market, but most of these smaller home keyboards are likely to not have a touch-sensitive keyboard. Yamaha used to make a synthesizer called the MX-49 that has a 4 octave keyboard that I believe is touch sensitive. That could be a possibility, but it doesn't have built-in speakers, so you'd have to used headphones on the go, and I don't think it could run on batteries, so you could only use it where there you have an AC plug.
Going smaller than that, to a 3 octave keyboard (which is what the PSS-A50 has) would certainly have some limitations, as it would limit what you could play with two hands just because of the size of the keyboard. But it would not be impossible, and as long as you are just using it as a supplemental learning instrument to use portably, and not as your sole learning instrument, then you could use a small 3 octave keyboard for practice -- but again, I would recommend something with full sized keys, not mini-keys. That would be difficult to find -- however, some small synthesizers do exist with 3 octave keyboards, but they will be considerably more expensive than the PSS-A50, they mostly would not have a built in speaker, and most will not run on batteries.
So, it all comes down to compromise. It depends how much you intend to carry around this keyboard, which would then dictate how small you would want it to be. And it also depends on how important built-in speakers and the ability to play it on batteries is for you.
Beyond that, the suggestion to learn how to finger actual chords is an excellent suggestion, and is in fact how I started learning how to play keyboards. My teacher started me with major, minor, diminished, and 7th chords, and then I gradually learned more complex chords from there.