Back when I was a total makeup noob, I saw an article on Clumps of Mascara which taught you how to depot your UDPP.
Being the over zealous thing that I am, I decided to depot mine. This was despite the fact that I hadn't even hit "pan" on it.
I only realised recently that mine had dried out and I was very reluctant to chuck it.
I bought this brush from Boots with my £5 off voucher (it cost me £1.50) and was quite let down by how well it worked on my eyeshadows.
UDPP and it worked a charm. You just stroke the primer with it and apply it to your lids, it works really well. You don't need to blend it or anything..and you don't get that chalky rubby bit either. It doesn't work on the primer if it isn't dried out (I tried it on my cousin's one), you get too much on the brush but if it has dried out then it works perfectly.
Try it, it really works! If you've got the £5 off voucher, have a dried up pot of UDPP and can't decide what to buy from Boots, get this brush and kill a million birds with one stone. You won't be sorry!