Make sure you get the kind that float. You never want the inside piece to touch the sand. It will grab some of the granules and will be rubbed into your glass. If you follow that rule, they are very effective.
I have a floating magnet cleaner that takes care of most things on the inside glass, about once a month I use a fresh razor blade to get bits of coralline and the corners where the magnet doesn't reach well.
Just make sure you buy the one for glass tanks, or acrylic based on what you have.
They work great, but from time to time you will need to scrub the couple of inches close to the sand line. I use a scrubby pad, because I am afraid if I use a razor blade I will cut an animal.
I use three things....
Soft cloth for film algae. A kent aqua-mop or those algae mitts do great.
A magnet (one of those from Algae Free) for regular cleaning.
Kent pro-scraper for coralline.
What I really, really miss though is an item I used to have years ago which seems to have since been discontinued.... the Dynamic Disk. I used to swear by that thing. Could clean everything short of coralline and do the entire tank in seconds.