As a machine polishing newbie, I bought the Halfords machine today, £85, and some G3 Professional SuperGloss wax, £27. I already had some G3 yellow compound sitting around, so used that instead of posh branded stuff.
Took me 6 hours to machine it and wax it. I am by no means a detailer and could have spent longer on it, but the swirls came out pretty quickly with a yellow (medium) pad.
There isn't a lot I can say about the Halfords DA as I have nothing to compare it to, but it certainly works well enough for me. Feels robust, pretty light, 5M cable and seemed to handle fairly heavy pressure no probs. I soaked it in water several times whilst rinsing the pad out and it handled that as well.
It's difficult taking pictures in the sun with a phone, but I don't think it has come up too bad at all for cheap stuff