I've used Nunn a fair bit but to be honest its a bit pricey and I don't think I'll bother getting anymore after my current supply runs out.
Its cheaper than lucozade? £5 gets you 12 tablets x 500mls so roughly 42 pence per bottle.
Saying that I only use it for long races or hangovers and if I used every ride/run then the price would start adding up.
to the OP, suppose you got to decide what you want first. Energy drink or hydration drink. Can't really compare SIS Go or owt like that with Nuun as they are meant to do different things.
I would also dilute more than the recommended amount if in a hydration pack, or alternate between water and nuun if in a bottle. Can get a bit much albeit easier on the stomach than carb drinks.