I have it and use it in my 2.5 gallon tanks. I was worried about it sucking up too much water too fast also. I went ahead and bought it. I agree, it does suck up too much water too fast. But I also believe it is still a very useful piece of equipment.
How I do my water changes is. I use a Turkey Baster (really does work) to suck up all the debris at the bottom of the tank. By the time I am done doing that, I haven't taken out a quarter of the water I need to. This is where the gravel cleaner comes in handy. I use it to suck up the rest of the water I need to take out and also use it to suck up anything I missed. The fact it sucks the water out too fast, makes for very short water changes.
I believe it is a very good buy if you plan to use the method above. But, if you want to use it solely as a gravel vac. No, it does not work.