Orion,
The diameter of the base of the pump is 1 7/8" and the pump is about 4" tall.
I've had the 3152 for about a month and it works great so far.
Only problem is if you have a small tank with plastic trim at the top. With the magnet mount, the water level will be about 3/4" below the top of the magnet. I have a standard 10 gal Perfecto tank and the bottom of the plastic trim is only about 3/8" below the inside plastic lip. So the water level would be about 3/8" below the bottom of the plastic trim. I don't like to see the water line below the trim, so I built an acrylic housing that hangs on the side of the tank and allows the magnet to sit higher so the water line is hidden by the plastic trim.
This would not be a problem with a rimless tank or when using a sump. My 10 gal is temporary and I will have a sump on my new tank, so it will not be an issue once I upgrade.
The 3152 only has one float switch, but the controller is programed to shut the pump off after 1.8 minutes to keep from flooding in case the float switch gets stuck. I tested it before I hooked it up to the tank and the pump shut off as it was supposed to.
Hope this helps,
Ron