That's what I'm trying to figure out. Why go away from the internal battery. I see that there is IMO maybe:
65% battery/mech mods ( stingray, IPV, sigalei, sx yihi, dna, etc.)
compared to 35% internal battery mods (iStick, MVP, etc)
I want to blow bigger clouds (than in my nautilus Minis) and get better flavor, longer batt, more efficient and built-to-last mod.
I know that a big part of this is getting an Rba or better tank system
I should also state that I use a 50/50 pg/vg blend. 12ml.
You don't need to move to a replaceable battery mod to do any of the things you're interested in.
The main reasons people like to use replaceable battery devices are a) because of longevity (in the case of mechs which have no circuitry to fail) and b) to have many extra batteries on hand and not have to wait for the device to charge in order to use it (not a huge problem with passthrough devices but some find using devices while plugged in annoying)
With mechanicals, there is no circuitry to fail so a good one can last years with simple user maintenance. But they also don't have any safeguards for protection from shorts, etc. You must learn about battery safety, ohms law, etc., in order to use a mechanical device safely.
With a regulated replaceable battery mod there is safety protection. Your device won't work or will give a warning if the coil isn't good. But there is probably a limit on how low you can build your coil, although with the newer devices that limit is much lower than it used to be. And there is a chance that the circuitry could fail but a good device should last a while. You can control the wattage &/or voltage without having to change coil resistance, which is a nice thing.
Personally, I would probably not bother paying for a changeable battery regulated mod since there are plenty of good devices with large internal batteries. I would pay for a good mechanical mod though just for longevity. It's nice to have a device I know will work years from now.
Just some things to think about.