Well, there is a reason why so many people do things a certain specific way. And trust me, it's not because it's 'cool' or it's the 'popular' thing to do.
It's because it works and is the safest.
Sure you can say an unregulated mat hasn't malfunctioned or your friend's cousin's great great uncle's chihuahua's friend has used unregulated pads for years with no issue. They are LUCKY! Damn Lucky! You hear horrible events of unregulated pads destroying entire collections and years of hard work going down the drain from accidents like that in this hobby.
There is still that risk of burning your animal, melting your enclosure, or starting a fire with those unregulated heating elements.
Why NOT use a thermostat? Why not give yourself that extra blanket of security and safety? Why even leave your animals to that risk?? It could be a small risk, it could be a large risk. Either way, still something I do not want to risk. Paying for a thermostat sure beats paying for vet bills and dealing with an injured animal. It 100x better than having part of your house burn down.