I'd be careful about the copies of the Jet Fin, most of them are crap. It's just "rubber" but the specific compound makes a world of difference in terms of feel, responsiveness, and energy storage and release.
The only one I ever felt compared well to the Jet Fin was the OMS Slipstream. It's a lighter monoprene version of the Jet Fin but still wears very well and feels almost identical in the water, despite being a little stiffer. I actually dive the Slipstreams a ot more than my Jets now, due to the lighter weight and better trim they allow in my current configuration.
The only one I ever felt compared well to the Jet Fin was the OMS Slipstream. It's a lighter monoprene version of the Jet Fin but still wears very well and feels almost identical in the water, despite being a little stiffer. I actually dive the Slipstreams a ot more than my Jets now, due to the lighter weight and better trim they allow in my current configuration.