I bought one and it works great. I have a tempurpedic mattress on top of a box spring. I put it between the box spring at a slight angle pointing towards the corner I want to lift. Some people buy 2 so they can lift one whole end of the bed at a time, which would be more efficient, but try it out with one first to see if you like it.
Note that if your bed is lengthwise against a wall, it won't help you for the corner(s) of the bed that are up against the corners of the wall, unless you have an easy way to pull your bed out (e.g., wheels).