DryGuy TurboDry Shoe Dryer Warmer
Please ignore that ignorant 1-star review.
DryGuy is the leading manufacturer of boot/shoe dryers. I have used their original Circulator driers (no longer manufactured, but at least for now still available (DryGuy Circulator Footwear Dryer Warmer). I have been pleased with the three of them I've used for several years. They have the advantage of being quite compact, and silent. If you want the equivalent from current production, you'll want to get the DryStix driers (not currently available on Amazon). However, I somehow lost two of my three driers, so got two of these units.
These units have the disadvantage compared with the DryStix that they bulk and weigh about twice as much, but have corresponding advantages.
First, they have work on both AC and DC (cigarette-lighter plug). Second, unlike my initial driers, or the DryStix, they don't rely on passive convection, the have a fan at the toe-end of the drier. Yes, it makes a little noise, but look at this way - it saves you the cost of a white-noise generator. The noise is soft, not objectionable and quite soothing.
Now, as far as drying efficiency.
Shoes and boots vary widely in how long they take to dry. My Salomon Men's XA PRO 3D MID GTX Trail Runner boots are so thin and light that they dry quickly. My custom Limmer traditional Italian-leather boots take a _long_ time to dry. My daughter's The North Face Nuptse Fur II Girls Boots 2012 take forever to dry by any method. Though my daughter likes them, they are not designed for cold-wet conditions, and are basically sponges for your feet.
Fixed dryers work best, but for portable dryers, you can't beat these. Unlike that first reviewer, don't expect them to work miracles. These work several times as fast as stuffing them with newspaper and sticking them in a warm place. And, unlike drying in front of a fire, they won't damage your boots. If the DryStix dry as well as my old passive-convection driers, then these with the fans work almost twice as well. (Having one of the old ones and two of the new ones allowed some side-to-side comparisons.)