I highly doubt most stove --> thermal cooker heat transfers are very efficient. A large percentage of the heat there gets lost, if you don't believe me put your hand on the stove after you turn it off sometime ;)
If you had a kill-a-watt you could measure, too, and I suspect you'd find that while a stove might run less, any electric stove uses a ton more energy than a pressure cooker. Quick googling suggests that a stove uses about 1.5x as much energy as a pressure cooker max does, so running the pressure cooker seems likely to be much less energy overall unless you run it for a loong time.
Most plugin-electric pressure cookers use about 800-1500 watts of electricity during use. Most medium and small stove top burners are also within that range (the larger burners use much more). It doesn't matter whether the heat is transferred in full to the pot or not. What matters most is how long you are using that amount of electricity for. I am assuming (I could be wrong) that you're using the pressure cooker on average for about 20 minutes to cook a meal. Certainly it is dependant on the food you're cooking and some things may certainly be more efficient to cook in a plugin pressure cooker. Strictly steaming vegetables, for example, only take a handful of minutes to cook in a pressure cooker and so may be better served with one. However, soups with whole grains and/or meats would take at least 20 minutes to cook with a pressure cooker in which case the thermal cooker would serve better.
I compare an electric stove with an electric pressure cooker because the comparison is easier, but gas stoves are much more efficient and so using a gas stove serves a thermal cooker better.
But, if the most amount of time I'm ever actually using a heating element with my thermal cooker is 10 minutes to a boil, then it is still a very energy efficient method of cooking that is on par with a pressure cooker for most recipes.
You can also just take any pressure cooker off the stove and wrap it in insulation (a blanket) and get the same effect
If I didn't already have a regular pressure cooker, I'd get the instant pot deal in a second. I like the versatility of my cooker, but don't like monitoring the pressure - it's so efficient that my minimum flame is usually high enough to over pressure and I have to alternate between off and on for long recipes. Instant pot is set and forget
You can't just wrap a pot in a blanket and expect it to continue to cook like a thermal cooker. Thermal cookers use vacuum insulation that lets virtually no heat escape. I can take a pot right off the stove and put it in the thermal container and it will be cool to the touch. If you attempt to wrap a pot in a blanket expecting it to thermal cook, then your food will quickly cool to room temperature and will not be safe to eat.
At any rate, I figured I'd just post some info on thermal cookers since most people have no idea about the benefits of them and how great they can be. Pressure cookers are great too (I used to run a website for pressure cookers).