. You should pick one up for anywhere between 20 and 30 quid I'd think. They are a relatively low output battery, but they do the job well enough - and as you note are much smaller than a conventional type and you can stick 'em anywhere you like. Even upside down if you fancy! They are about half a kilo ligher than a conventional type battery too.
My only concern would be that NSRs seem to like a good charge in the battery in order to fire up. The 3XV battery might be a bit anemic in comparison to a 'proper' battery. If they work OK on the NSR though, I'd think it a useful mod if you are wanting to lose weight (from the bike
) or relocate the battery.
Cheers
Wb