I needed to grind/hone a crappy block plane edge and it's a lot easier by hand with the help of a little handle - you can get more pressure on it and it's much faster. You can see how crap the blade is, but improving.
This handle took a few minutes to make from a bit of scrap, but this time I added a "nose".


The end of the nose just clears the blade edge at an angle of 30 degrees

So you can only hone at 30 degrees or under

You can see it better here

It works like a dream. Fast and easy. Tilt it back to grind on a coarse stone, tilt it forwards to hone on a fine one. It produces a rounded bevel with an edge precisely limited to 30 (or however you set it). For those who can't understand that concept it can produce a flat bevel, but there is no particular point in that.
I wondered about developing it. You could add wheels at the front (front wheel drive) and a bit of adjustment in the blade holding. It wants to be quick and easy so the slot is good, but perhaps a magnet or something, so it'd sit on top of a chisel. But it's good enough as it is, and I can just knock up another one for a different blade/angle etc.
In principle it solves all the problems associated with conventional jigs, and also can be used on any medium, scary sharp etc.