I'm not so sure about that...

If you're proficient with a keyboard then you don't need EZkeys... and, personally, I find it much easier to just play a real bass.

What I would like is a keyboard with a bunch of very "realistic" sampled sounds. Sax with breath and key noises for example, that sounds "natural" across the entire keyboard.

If you can download that onto your computer then you should be able to find a keyboard "pre-loaded". Everything "Internet" based has become such a rip-off... They engineer "incompatibility" and "expiration" into their products just to keep you buying more and more crap.