Strictly speaking, the Space Cadet keyboard was JLK's creation (John L Kulp, who ran the MIT Plasma Labs computing facilities, and who went on to help found Symbolics when they split off from the AI Lab).

I had a Space Cadet on my desk in the EECS department along with a Plasma TV system monitor.

Had fun times hacking the PDP-11 software driving the Plasma TV system.

I wish they still made keyboards like that. I'm curious to know the "feel"

As gumby says, the Space Cadet keyboards, being Microswitch Hall effect-based, were a bit spongy due to the big plastic case, but the switches themselves were dreamy.

But the whole experience was still not as satisfying as the original Knight keyboards, I suspect because the Knight boards used the original, larger switches, while the Space Cadets used the smaller. Chyrosran22 on Youtube explains all this (https://www.youtube.com/watch?v=pcdN4Vzg6_g and https://www.youtube.com/watch?v=oDozftThFMw).

By the way, after 40 years of despairing over the loss of Hall effect switches (I nursed a Space Cadet Livermore Labs clone from a group buy for some years into the mid-80's), there are now two keyboards using this technology, and I'm loving the one that's actually available.

Steelseries Apex Pro is what's now shipping, and it's a dream. (https://www.amazon.com/SteelSeries-Apex-Mechanical-Gaming-Ke...)

The Input Club Keystone is still coming, slowly (https://kono.store/products/keystone-analog-mechanical-keybo...), but I'm also really looking forward to trying it.

The CADR space cadet had a spongy feel, probably because of the large size and plastic case. A sad dependent of the Knight TV keyboards. With the 3600 series Symbolics replaced that with a solid keyboard (fewer keys though) that was more satisfying to type on.

Some of those keys like thumbs up/down etc were never really used anyway.

I see they have convenient up/down vote keys on the righthand side of the board.