Hi
My tank came with a standard gravel vac which I used at first. Using it, I would syphon the water and vacuum any debris from the sand at the same time. This works very well however, I found that midweek the sand would need a quick tidy up but I wasn't wanting to do a water change. I then bought one of the marina battery powered vacuums. It recirculates the water and catches the debris in a cotton bag.
Like you, I had read a few bad reviews about these but decided to go for it anyway. I'm really glad I did. Sure, the suction is no way near as powerful as the one I do water changes with but it picks all loose debris up. Sometimes it needs a little encouragement to kick up the debris a little before it will suck it up the tube.
I've heard lots of good things about the python that others have suggested but I'm not sure if you can vac with it without removing water. Maybe the others could confirm this. For me, I do a water change once a week and a vacuum midweek and the way I do it with the above equipment is perfect. I'm really glad I bought it. I think it was £25.
If you want a battery operated one that is for doing water changes I don't think it would be great. Perfect for picking up debris but I can't see the one I have ever being powerful enough to syphon and I would much rather use something else for that purpose.
David