I love my siphon with the pump but I learned a lesson the hard way this weekend....make sure there is nothing that is small enough to get sucked up but big enough to get stuck in the bulb! I sucked up a baby moss ball and it got stuck inside of the bulb. I had to find a very long straw and push it through to force the moss ball out. It was a real struggle. The moss ball ended up getting shredded.
I also think it's harder to start a siphon on the smaller tanks. They are usually not deep enough to fully submerge the gravel vac and that makes it harder to start.