As far as I am aware (after a quick google search) the fluval 3 is rated for tanks upto 90cm which is much bigger than your 10g (think it'll be in the region of 20-25g) so it should be fine.
What were you going to filter the tank with if you'd not been offered this one?
I actually voted for the fluval for the very reason its rated for a bigger tank, the others would all be rated for a 10g. You cant really over filter a tank (providing water flow isn't to much for the fish you've got) so if its free I would get it.
The only problem i can see it the phyiscal sizer of it, I have a 10g and some filters look stupid in them because they are just so big. E.g. The interpet PF range. Ive not seen the fluval one 'in the flesh' but I have found some new fitlers IMO lack the spunge capasity (although in the case of the interpet ones this is replaced by the ceramic disk things), which is the most important part of any fitler IMO.
Hope this helps. Bottom line, get it, try it out, if it works great if not replace it then. No point spending the money now if you needn't
Sam