I have one of these too and they are incredibly good - the only thing I've ever found that actually works.
However, it's all about timing - if you've already started scratching and the itch is unbearable, some oral antihistamines will help.
Interestingly (and this is purely anecdotal, I have no science to back this up), some years ago I was travelling in a very mosquito-y area and started taking an oral VitB12 supplement and garlic capsules about a month in advance.
Normally I'm a bitey thing buffet, but on this occasion, although I still got the odd bite, they were far fewer than normal and I wasn't as reactive.
As I say, this is purely my experience and I know that correlation does not necessarily equal causation, but it seemed to work for me.