I currently use an App called ONE MEASURE. It simply sits on your phone and I assume monitors activity use. It doesn't pay much on a day to day basis, 16p. But you forget you have it and before long (£5) you can cash out to a voucher. A fair few to choose from with supermarkets also available. It doesn't misbehave like the Nielsen App nor does it slow your phone down. Payout is guaranteed so along with the Incompass media panel (£5) and another one I have (although the name escapes me right now!), it's £15.00 to add onto survey earnings which can be often erratic.