I've decided against the Stingray now and the two filters I have in mind are the Fluval U2 and the Eheim Pick Up 2010. The Eheim has a higher LPH but is adjustable so shouldn't be a problem. Both are the same price on Ebay, if not a £1 cheaper for the Eheim and if what I've learnt so far about Eheim is true, they are to be trusted.
Can anyone with experience with either of those two filters tell me if they're suited to a 51gal<(oops, LITRES!) tank with small fish?