I play the lumatone (https://www.lumatone.io/) which is very similar.

I personally love it, especially as I like to do a lot of improv in various tunings, and the layout makes transposing and thinking about structure so much easier than a traditional keyboard. The terpstra seems similar, not sure what their selling point is over the lumatone.

Edit: oh, it seems that the lumatone is the commercialized version essentially. Great hardware, can reccomend!