To start, I have a thin build (5'10, 150 lbs) and my ankles are no exception. Boot is a Fischer Soma Progressor 120 FWIW. Shell is 25.5/293 mm for a 9.5 foot size. Couldn't have gone any smaller. Generally fits well. When I tighten the top buckles of my boots to where I need to be, it's actually somewhat hard to shut them without my foot in the boot. I find this strange as the bolt can still be moved over a notch but that's how it is.
I've only given them one test day so far but they really seem to do the trick. Cheap ($20ish) and easy. I now barely have to buckle the tops and I have a nice secure fit. They also took out some of the bootpack as the bottom portion does curve around the tongue and go over your upper foot a bit. As a result, I'm tightening the lower buckles one notch less than before. I feel less presure but a tighter fit.
In some respects, I wondered if these would soften up the boot a bit and make it less reactive. Foam compresses and one would think more foam would lead to a lower end boot feel (or lack of). This hasn't been the case. Maybe because the extra foam is somewhat firm and only in the front. The sides could actually be a tighter fit. Whatever the case, if you have a similar build/issues, you can't beat giving them a shot for the money.