i would much rather fit an aftermarket heater than use a heated liner in our store, if the liner goes wrong then you have to replace the liner and do all the fitting work again, if the aftermarket heater system goes wrong its either the element (cheap and simple to replace) or the battery (not so cheap) past experience is these things go wrong a little too often to want to have to try and get warranty from the suppliers of expensive liners especially when they announce they no longer make the liner or they don't have any stock
keep it simple
Yes, CEM has correctly stated logical facts!
The reason that there are durability complaints about the various boot heaters available comes down to poorly installed heaters. For example having the the cable come straight down the middle of the footbed from the heat pad at the toe, and exiting in the direct center of the liner heel and coming straight up the back of the boot. This type of install will expose the wiring to. multiple wear points that will inevitably wear through the cable.
So the purpose for getting the wiring away from your body weight and pressure through the footbed is the best way to get your heaters to last. It does not have to be done as in the video that Mike Thomas posted. The installer only has to be slightly smarter that a bundle of copper wires. You can come straight out of the toe and routed on the top of the liner avoiding the boney spots like 1st and 5th metatarsal heads, styloid process, navicular, and ankle bones. Like any other fitting objective in ski boots the key is to redistribute pressure to alleviate pain.
To CEM's point about built in heat within the liner... I would definitely be cautious to jump into that game. History has shown anytime a ski boot supplier has attempted to have any type of wiring running through an inner boot, it has been a failure. In common sense terms the companies that specialize in boot heaters and have been selling and improving them for over 30 years have yet to idiot proof the product or the process. What would be the indicator that Rossignol, K2, or any other boot supplier would hit it out of the park on their first attempt. Not saying it couldn't happen, just saying I would wait until the product has survived a season or 2 before throwing out good money on a liner that will either have to be replaced from the manufacturer as warranty or at either a cost to you for the product and or product plus shipping including down time where you have no boot to ski on waiting for a warranty from a company that post COVID can barely deliver ordered product, much less excess warranty parts... ( Just in case you have not seen the paradigm shift in product innovation and delivery during COVID ) I would either put my eggs into Hotronics, or Thermic basket, or look into some of the same companies that are making heat built into socks ( those seem to be passing the smell test of durability and performance ) Also includes independent brands like Lenz.