It's not often I review something like this, but it is simply the best medicated product I have ever used.
I don't really suffer from dry or chapped lips chronically, but my lips tend to damage quite easily in situations where I'm dehydrated, unwell or have just put my body through strain (strenuous exercise, raves, festivals etc.) I always turn to this product as soon as I can when I feel the lips need proper repair, rather than just the subtle moisturising treatment of a regular lipbalm.
It comes out of the tube easily and actually feels cool and refreshing on the lips, which when damaged are often quite hot and irritable. It's pretty much invisible when rubbed in, giving the lips an extra moist look but no obvious signs that you've put something on them.
The first thing to note is how quickly this stuff works. Your lips feel better within minutes of applying them (I'm sure this is just a moisturising effect rather than anything medicated, but it's still impressive). If your lips are cracked or chapped when you go to bed, put on a decent helping of Blistex and you'll awake the next morning with them pretty much fully healed. Reapplying frequently during the day can make a vast improvement in mere hours to lips that are in very bad condition.
I haven't tried this product on cold sores, which I would imagine to be tough opponents, but have confidence that it would do some good.
I'm always quite sceptical of products like this because although I accept that they do work in most cases, I often feel like they don't significantly speed up the healing process enough to be worth the money. But here, 2 quid a tube seems an absolute bargain.