Hiya subway! brrrrr 25, that's way too cold.
Don't take this to the bank at all, many things about all this that I don't have right, but my understanding is that a mech mod sorta works more naturally with your batteries and is much easier on them. Ohm's law, x ohms and x volts produce x watts.
With a mech mod, as your battery decreases in volts, your wattage decreases. You set your watts, by how high or low you build your coils, (ohms) and how low you allow your battery to get before changing it.
with a regulated mod, you set your watts, and it stays at that as your battery decreases in volts. So it's forcing your battery to produce an amount of watts that it really doesn't want to produce. Now I don't know where the amps fit into all this and batts are rated with amp ratings so they don't blow up etc, so the batteries are able to do what a regulated mod is making them do when you set your watts, but it's harder on the batteries from my understanding.
Some folks think regulated mods are safer cuz they have safety mechanisms built in that they won't fire if you're asking it to do more than is safe for your batteries. But those are built in a chip that can fail. In a REO the spring is your safety mechanism, it doesn't rely on a chip. if you get a hard short, the spring will collapse, and the battery will drop away so that the firing pin can't reach it and it can't continue firing. You can lock the firing button so nothing falls on it and causes it to fire continuously because you don't have a 10 second cut off like regulated mods do. And if a battery does vent, you have a huge squonk hole for it to vent through, not a tiny pin hole that you find on many or most tube mech mods. Hope that helps, and hope I'm right about all that, if not, I'll blame sleep deprivation