I use one and it works fine. Most guys on here feel you need to spend a ton of money for one or they are no good.
Here's how to use it....turn your amp up to where it sound best to you. It might be halfway, all the way up or whatever. If the amp is too loud, start backing down the Hotplate till you get the level you need. There are eq switches you can play with, but I dont find them useful.
If your amp sounds bad cranked, it will sound bad cranked and attenuated.