3 months experience with M401:
Atomizer life on batteries only: 24, 21, and 29 days - average 25 days till death. Current atty on batteries has been going 19 days so far. Vapor quality usually drops off in 10-14 days. Cleaning w/alcohol helps that a little.
Atomizer life on passthrough: 13, 8, 8, 7, 14 days - average 10 days till death. And that's with using it only half time (used separate atty on batteries the other half). No obvious pattern whether cleaning lengthens or shortens life, except if you try the hot burn cleaning method on the passthrough, which can quickly fry the atomizer.
Passthrough eats up cartridge liquid in a big hurry, with a lot of it wasted condensing inside the cartridge. Lots of great vapor while it lasts though. If you puff too much to use the last bits of liquid in the cart, you are likely to fry the atomizer, so I try not to let it dry out. (See info about "hot burn", above.) My conclusion: M401 passthrough provides a bit too much power.
Got a Joye 510 5 weeks ago. Using it about 50/50 with M401. Original atomizer still in excellent condition. Have cleaned it w/alcohol twice when vapor dropped off a bit and that brought it right back to life. It's great except for constantly having to change/charge batteries. Also, 510 cartridges only wick about half of the liquid out after they've been refilled 4-5 times, then the vapor gets really weak. Cleaning the wick material doesn't seem to fix this. After I get tired of topping them off all the time, I start with a new one. (I'll have to try replacing the wicks at some point.) On the other hand, I've refilled M401 carts 10-15 times and they still get all the liquid (what little it holds) to the atomizer.