The good: fantastic design and build quality. Magneto/optical key sensors way better than any key switch on a normal keyboard. Really surprisingly easy to learn and adjust to "almost-qwerty" default layout. Nice for long-form typing, fingers roll around very short movements, very comfortably.
The bad: huge on a desk, they are really chunky boxes and there's a big power supply and controller box. Basically unusable for one-handed hunt-and-peck typing. Really annoying to use as a mouse (can be done - one side middle finger does big movements, the other side does fine movements, but it's still stepped keyboard-based-mousing), but also annoying to move hand from keyboard to mouse and back because it involves careful lifting of fingers out of, or into, the key-wells - fingers are surrounded by keys you don't want to press. Because of that, can't hover hand over keyboard. Ever. Awkward unless you have perfect typing style - can't habitually press a key with the "wrong" finger, now there's a correct finger for every key and no other option. Expensive even then before their big price hikes and production problems, even second hand.