They are great keyboards, you become a little tied in to the Native Instruments eco system to get the best out of them though, is the only downside.
It’s best features shine when used with Komplete Kontrol plugin (Which wraps other plugins inside).
The keys and quality of controller is superb though. I love using mine, and the light guide is a really nice aid if you want to practise new scales, or use sample libraries with splits which Komplete Kontrol controls for you. i.e. it’s very good when using Battery, Abbey Road drummer etc. - all coloured as to which drums are where.
Also i really like the integration with Cubase’s mixer, even though faders would make more sense for volume control, using the knobs is really good as you don’t have to ‘catch’ to the correct value as you would a fader, as they’re relative/endless knobs. The interface is nice and quick also, which makes them very useable.
Also, in regards to price, i think it’s quite common to see NI controllers go on sale, i don’t think 20% off is anything spectacular in all honesty. I’ve seen some really good offers via reverb.com direct from Native Instruments in the past - that’s where i got mine, but they don’t seem to have any listings right now.
As a vanilla controller (i.e. if you don’t plan to use Komplete Kontrol) they’re definitely less featured, but still a great keybed. The Arturia Keylab Mk2 would be a better choice for a vanilla controller, again great build and feel.