I ordered 4 of these motors at a total cost of £20 delivered (£5 each) and I am incredibly impressed. They are very nicely made, run on double ball race bearings, have nice large carbon replaceable bushes and are all but totally silent and vibration free.
They are 51mm diameter and have a body length of 71mm. The output shaft is 8mm. This makes them about the same size as a Speed 900 although they are rather softer motors.
Testing on 12v (ignoring the 24v bit completely) they all run, on my 5amp 24v bench supply set to 12v at 0.4 amps (slightly less on 7.4v) out of the box at 3600rpm. Connected to a 12v car battery they stall at around 7.5 - 8Amps with loads or torque. The spec says that they weigh 460gms.
Following my usual mantra that loaded rpm should be around 65%-75% of free running rpm these would be turning at 2400 -2700rpm. This is fine for the sort of modelling that I do.
I am thinking 55mm 3 blade on 11.4v unless anyone think that I am mad and I am aiming for a current draw of around 3amps. I would go larger if I thought that I could within my amps limit
I note that the place that I ordered them from was so impressed with my order that they are now the same price an everyone else at around £10.