Personally I think they are gimmicks.  Sure, OK, they DO work for a run or two, butt that's it and from my experience, they are not all that great for the base of your board.  The base of your board is designed to hold real hot wax, nothing else.  Maybe carry a rub-on wax for emergencies (yes, some times you REALLY need a good slide).  Myself, I carry a chunk or two of real hot wax in a zip-loc bag in my pocket and rub on as needed.  Yeh, it only lasts a run or so as well, but so do the others and it is much better for the base.  At least it will get you down the hill to the shop where they can do a good quick hot waxing for ya.