those halfords polishers are crap, you won't get any real correction done with them, my neighbour has one, I tried it once and got worse results than by hand.
the silverline is a rotary, so there is potential to totally wreck your paint with it, so I'd recommend reading a lot of guides etc and get a practice panel to work on before attacking your car with it. It may only be £20-30 but by the time you have bought pads, polishes, backing plates, work lamp, masking tape, buffing towels...you'll be looking at the guts of £200 if you get semi-decent kit.
also be warned, if you're a wimp you'll struggle as the silverline weighs a tonne