When I first started I had the opinion that a Powerhead is a powerhead and just moves water.
Since I got my MP10 for my 28g I will never go back to another power head. I already have an MP40 for my new tank. The Echotech's have the actual motor on the outside of the glass and the propeller on the inside. This does 2 things, does not put any extra heat in the water, and also saves a ton of space.
If I didn't have the Echotechs, I would prob have gone with the Korilias. The Echotechs are also SILENT! and very controllable. I am not saying that you can't control other power heads, but not like the echotechs IMO.
They are big bucks for a power head, but one could replace multiple of others.
Ebay is great for some things, but I have found that you get what you pay for. You also have to be careful of any electrical leakage (prob not the right term) which can effect your livestock. Flow is one of the most important things IMO, so anyway you decide make sure that you have enough of it.