Put wireless weatherstation's outdoor temp sensor to where cats are to see what kind of temperatures there really are. No wires or holes required, but range might be reduced a bit.
Too much warm is not good either, that is going to make them feel really cold when getting outside again, so some temp is good and with good ventilation is better as they can dry their feet after walking on snow.
Same basic principles apply as with house building, so putting some heater to where cold air enters the shelter makes all air warm, air should have exit hole high up and size of hole(s) will determine how much air is changing. Our building rules had statement of changing indoor air being somewhere around 2.5 times in 24 hours, which of course is not constant with gravity based air circulation, greater the temperature difference, greater will be rate of air flow.
Problem with cat shelters is water content in air, humidity, exhaling mammal produces quite bit of water at every breath, cats being evolved in desert are better in this, they would not survive at desert if they would blow as much water out as humans do, but they still do quite a bit.
My ferals experienced this as my shelter had poor air circulation, flap which acted as door tended to freeze shut and it got easily 1/2" layer of ice on it (in a day) as water vapour in air freezed to cold surface (the flap), of course part was because snow and ice they brought in at their feet, but it was really good example what will happen when there is only one entrance covered with flap, even that flap had holes in it, it did not helped too much.
Of course it was an issue at colder times, not so much at warmer times, we had almost -40C for a coldest week, yet at times cats decided to sit on top of shelter instead being inside, that was because humidity was too great inside, at least that is what I could point being a reason as when I put my hand in it was quite damp in there, air was like if it would been possible to fill a glass of water from it.
Straw etc has abitily to take in water, but where that water goes then? Replacing straw would solve that, but without replacing water has to go somewhere or it will stay in straw, which is bad as things start soon to grow in it.
Feral Villa's manufacturer web site says that heater is not needed unless most severe conditions, when I checked data from Illinois weather, coldest day was -21C in data, so we can assume that is what manufacturer means by most severe weather as there are other remarks on site that state manufacturer's point of view is Illinois weather and conditions, if one lives at warmer area need of warming is probably less and if at colder area need of warming is probably greater.
Claims made are often quite subjective and knowing bit background helps to put claims to proper perspective to one's situation.
Luckily cats are quite adaptable and if they can find some shelter from weather they will do fine, wind and rain are worst, then wet ground is quite horrible enemy, but temperatures themself are not very big issue for cats used to live outside.
I have to design shelters here for double as cold weather what is in Illinois, sadly I could not find any usable data about Feral Villa's insulation, thickness and material would be needed to do any kind of estimation how well it will handle the cold, so there can't really say much about it.
Temperature losses are however two kinds, one is with changing air and other is transmitting trough/via materials, job of insulation is to prevent these, radiative losses are quite small, so I would not put too much weight on reflective insulation, it is bit different when heating, scale is quite lot different. Most of insulations are utilizing technique where air is not allowed to move at insulation material, there are also NASA developed insulation that has vacuum in it, vacuum stops heat from escaping because there is nothing to transmit heat.
Salesman of course sales things, but it helps to know some basics so one is not so easily fooled, but as there is no enough data can't say it would be case with Feral Villa, also many kitties seem to live fine in it so that product probably works well enough, but there are many others where situation is not so good.
Oh and about the cord, they really seem not to mind about that one at least not my three, but then again my three is quite ignorant of many other things too which often are told to be sensitive things for kitties, they love if I grab them from tail for example
