I have gotten 2 of these, and they're really compact, plenty of flow, and have a prefilter to boot. adjustable flow rate, low voltage power supply, venturi... I love them. I packed the first one with filter media and burned it out over 6 months, and the second one i haven't mistreated, runs great, but I'm not currently using it in anything. The only drawback is that it doesn't seem like you can remove the impeller.
I could not find these for sale online, got mine in chinatown for around 25 bucks. I can see if they have more next time I'm in there or you can call Win aquarium on Mott St. NYC, he was importing them for a while and just selling off the stock.
and look at this (a little off topic) tiny pump I found while googling... if using 1/4" hoses and fittings was an option, this could be so sweet outside the tank! http://www.micropumps.co.uk/ probably a bit expensive in small quantities I'd imagine.
Isn't much to say about either really. I guess the part I really didn't care for with any small ones I've had. Is theres no flow direction adjusting at all.
only reason I could see would be if you were planning on breeding anything, fry might get sucked into the koralia pretty easy. I'm curious myself if they are too much flow for a 15, I like the way they look.