I think eyeshadow primer is definitely a good option for those who love wearing eyeshadow but find it either doesn't last all day, or they struggle to make the colours show properly on their eyelids. Using a primer helps to give an even base colour cancelling out veins, blue and red on the eyelid and also gives something for the eyeshadow to cling on to helping it to last longer. I usually go some form of liquid primer like the urban decay primer potion or the more affordable elf version (£1.95 and awesome) but more recently I've been using little pots of primer like this one from Avon. When I saw this NYX eyeshadow base primer on Isme I decided to try it out, plus I had a 50% discount code.
The eyeshadow base is actually a solid pot of product rather than a cream or mousse consistency, it reminds me of a solid balm. In colour it's white and very similar to the texture of NYX jumbo eye pencil in milk. Although it's a thick texture, it's easy to apply to the eyelids and I find using your finger to apply it works best as this almost warms the product up slightly. It gives a great even base for you to work with and really makes the eyeshadow shades more prominent and full of colour. In the swatch you can see that even a pale shimmering eyeshadow looks 'full on' on top of the primer. In terms of wear time, it definitely helps to keep the shadow in place all day without creasing - so a great option for oily skin too!
You can find NYX online, I think some Next stores stock NYX too but I got mine from Isme for £6 (plus I had 50% off, so an epic bargain there).