I'm running the 1578kn 1521 in my Revo on 5s and its is a sweet smooth and cool running motor. It is way more motor than you really need though. But wha tthe hell.
One thing to note is that it uses 4mm motor mount screws in the front so you standard motor mount will need to hav the holes opened up to take the 4mm screws. Other than that its about 1mm longer than a Lehner 1950, but its bigger in diameter than the 1950 with a bigger diameter rotor so it has even more torque. (like thats really necessary
)
Overall I think its a good motor, but you need to use its power with lower rpm and taller gearing vs. trying to spin that big boy at 35K rpm. The big motor will really pull the juice if you start spnning it really fast.