Eyelash curlers. You either use them or you don't. If you are a pro make-up artist then you should use them, should have them in your kit and it really is worth having a good pair. You can stop reading here.
If you are not a pro make-up artist then is it really worth spending money on something you can get for a couple of quid in your local chemist? Well as with everything there's no straight forward answer.
The problem with recommending eyelash curlers is that they are all slightly different shapes and eyes are all slightly different shapes. It may be that your eye shape exactly fits and suits the cheapest curler on the market. If so, and you have them, then there's no point rushing out and buying a more expensive pair just because I, or someone else, says so. The problem with a lot of curlers is they are too rounded which makes them uncomfortable to use - if you look at the more expensive (and popular) brands they are often less curved which makes them more likely to fit any eye shape and more comfortable to use.