[MultipleParadox]

Or you can get a new slide for your 4.3
Most after market slides will work with 5.1 sights/cocking handles

Note: I only fiddled with 4.3 so I don't know the differences between the stock 4.3 and 5.1 rear sight socket. Maybe they are indeed the same, and as mentioned above by GBBR, the "specific" 5.1 handles might be just to go on top of the Bomar style sight or something

And/or: most Chinese retailers, and many others, will just throw in a description like this without really caring about knowing if it does fits all 4.3 and 5.1. If the manufacturer tells them " this for 5.1 cock handle", well that's what they'll write, even if it would for the 4.3 accordingly.