The Best one from the late 60's thru the 70's was the Bianchi exerciser.
Folded up, had bars, saddle, cranks, and no wheel, used a flywheel, that was very heavy, like a auto drum brake, the resistance pad was on a spring steel lever that pressed a felt pad against the inside of the drum. Variable tension. Very smooth resistance. The flywheel spun via a chain and sprockets faster than the cranks.

These were very popular, so much that there was a waiting list for them, we would get in a batch and they were out the door. Bianchi just did not make enough of them!