That's basically what it is. It does dish out precise 10ml samples though. Can be a timesaver if you are running 5-6 tests on a couple (or more) tanks.
Instead of filling out the test tube to the 10ml line you just dump the pipetter in the tank, push on the knob and presto! You havve a precise 10ml sample. No fuss, no need to look at the line on the test tube.
They also generally use "ejectable" tips. So you are 100% certain that the previous sample you pulled will not contaminate the next sample.
Gerenrally, this thing is used in labs. I've never seen a 10ml pipetter. I've seen some 10µl, but never 10ml.
Can be usefull, I would gladly use one, but not buy one. To pricey for me.