I had a ZX Spectrum + and the keyboard was pretty decent was much better than the rubber of the normal one. The Sinclair ZX81 probably takes the cake for worst overall as it was just a very thin membrane.

I had original rubber key spectrum, they weren't horrible to touch but they were very slow to type on.

I had a +3. At the time it was much better than rubber 48K keys.

If you are expecting cherry mx switches, you will be disappointed.

I had a Sinclair QL which pioneered the keyboard. It wasn't great - it was far behind the Acorn BBCs and the Commodores) but it was quite usable.

There was significant vertical travel, and there was variation in the push the key gave back - increasing to a point of no return, then a quick downward movement to the thunk of the end of key travel.

I could type moderately fast on it.

The rubber keyboard was pretty weird first, felt a lot like cheap pocket calculator, but once you got used to the BASIC shortcuts, you could program like a champ on it.

You mean the original original ones? Yeah... they were honestly really icky and rather bad for typing on at speed. I type normally at 150+ wpm and the response speed was lacking and only slowed me down. Cleaning them was... not really an option. Not unless you wanted to spend a lot of time painstakingly taking the keycaps/membrane off and carefully putting it back. I'm honestly surprised to hear that anyone would want to recreate that fucking abominable experience. masochists