Even with Halfords vouchers you can use them at loads of different bike shops. Halfords will have a list on their website.
However you’ll probably struggle to find better value than the Boardman or Voodoo.
I’ve not studied the specs in detail (as when faced with a similar decision I was looking at full suss). However if I remember correctly, the Boardman will be lighter, a little more ‘trail’ than ‘all mountain’ (if you like marketing pigeon holes) and the Voodoo will be heavier, with more travel bigger front disk etc. I think the boardman will be 2×10 and the Voodoo 3×10 ?. So depends what you want to do with it and then any badge phobia you might have.