Anyone got one of these?

http://www.laptopshop.co.uk/SPS-slim60-laptop_battery-6063-1-b9.htm

It's an external laptop battery and should give me another 3-4 hours of playing. Anyone got one, used one? have any comments?

I can get two normal replacement batteries for that price.

Edit: just did a foogle search, and I can get 4

On my Hp laptop i have an extra travel battery wich is sort of similar. you attach it below the computer and the computer uses that battery first. it does give some extra hour or 2 of battery time. but its too clumsy and the extra battery tends to loose contact with the computer.
That said the one on the picture looks better than the travel battery for my laptop.

Problem is that I can't find a replacement battery for my laptop, it's either too new or too crap!

lol