A while ago I saw nuun advertised in a magazine, but could not find them in the UK. I emailed the company and they put me in touch with the UK distributor, who kindly said in exchange for a review they would send me some samples.
They sent me:

A bottle and 3 flavours to try. In each tube are 12 tabs, which should be dropped into 500ml water and left for 2 minutes before drinking. They fizz about loads but dissolve without stirring or shaking or anything.
According to the faq on the website “What is nuun?”;
- four essential electrolytes: sodium, potassium, magnesium & calcium
- a nice, refreshing flavour to remind you to keep drinking
- a bit of fizzy stuff to ensure it dissolves quickly without having to mix or shake
- a smidgen of colour in the form of riboflavin (vitamin b2) & beet juice depending on the flavour
- a sprinkling of love
Tri-Berry

The flavour was sweet and pleasant, so fine for drinking. I was glad it was not fizzy, so it was similar to drinking fruit squash. Of course the real benefit is the salts and electrolyes that are replaced by drinking this. I usually get a headache after a long run (which I am sure down to dehydration as my face is always covered in a thin layer of salt), no matter how much I drink (and try to eat salty things). I have never got on with lucozade or the science in sport drinks, but I did like this, and did not have a headache the first time I tried it.
So 10/10 cherries as although I would not choose flavoured water normally, after a run it was perfect to rehydrate with.
Citrus Fruit:

The flavour was similar to a weak lemon squash. I prefer the berry flavour, but this one was still nice. I had it while I was on a run and as it is not fizzy it was fine to drink while running. Again the tablet dissolved with no shaking or stirring needed which is always good.
8/10 cherries (I prefer the other flavour)
If you are after it in the UK you can get it from wiggle right here.
Orange and a hint of ginger;

This again dissolved perfectly, and gave the water a nice hint of orange flavour. It was not an artificial tasting orange like some can be (think frozen orange lollies) but more of a subtle orange taste. I could not taste the ginger (but I had eaten something else- I will try it again to see) but I liked the orange taste.
9/10 cherries
The tri berry is my fave flavour, but all 3 flavours are nice, refreshing, and more importantly are easy to drink after or during exercise. So thumbs up from me!