Piling onto udanijo's comments - I've got some head updates from actually trying to install them on a tank, not just screw them into the post. My notes:
Protank FAIL, Evod WIN.
The flange at the base of the Protank head seems to be a bit too wide for me to actually screw it into the Aro. I could pop it into the tank, but couldn't get the threads started with the Protank head screwed into the base.
Tried again with an Evod head pulled out of a Fasttech fake Evod - success. It also does indeed tighten up the draw and also seems to heat up the vape a bit. This could also be related to a different ohm coil - I've heard the Fasttech ones vary quite a bit and I don't have any kind of electronic metering devices.
Had a bit of a blowout when down below 0.5 ml of juice on one today - started gurgling, not from the typical overheating I'm used to from BCCs. Tried to hold the fire button and blow out the extra juice, instead of it coming out as vapor it puked quite a bit out through the carb holes. I've had this happen on occasion with Evods, so not incredibly surprising, but a touch disappointing.
Also, I didn't notice any metal shavings on cleanout, but I just used a hot water flush and a paper towel and pipe cleaner to wipe out - I could have missed it, as it seems much more likely they'd have been evident on a q-tip.
Will vape a half-tank with an Evod head (since I already filled it up) and report back with any issues.