Yup, they work great, but there are some things to keep in mind. They don't automatically shut off when the print is done, so if you leave a long run of banners overnight and it stops in the middle of the night, the heaters will probably melt the media or you may come to work to find a burned down building. We left ours sitting on a run of wallpaper for about 30 minutes once and it was starting to turn brown from the heat where it stopped. So you have to watch it closely and make sure you move it from the media when the prints stop.
Also, it takes a few minutes for it to warm up, so it's not really worth setting up for a shorter run. We don't really use ours for anything under 20' or so. It's ideal for long print runs where you're printing an entire roll of material, it's just cumbersome for short jobs.
But it does make a noticable improvement in dry time and ink durability, especially on banners and wallpaper. They're not cheap for what they are, but ours has proven a worthwhile investment.