Is getting the wheel out a PITA?

It's not difficult to get it out, but it can be a PITA to put it all back together on a dark cold muddy night if you needed to fix a flat.

I'm not sure you could get it to work on a horizontal drop out – because of the need to use the chain tug piece.

I've been using one of these on a Dawes Edge one frame for a few years. It works well but is fiddly to set up initially.

On the back side of the caliper plate is a recessed "Half-Hex" section that is intended to sit around the cup and cone lock-nut.
Then there is the two knurled surfaces on the plate and tug that lock into each other. The whole lot goes on the inside of the track end (You do have to adjust the spacing on your axle to accommodate the extra width, or stretch the stays apart to fit it in).

The rubber headed screw braces the whole set-up against the seat-stay when braking.