All those answers seem rather typical in my journeys thru the ecf forums, and are good ones for typical carto use. Guess I'm a bit different in that I get months out of them unless I'm using tobacco extracted juices...and in that case, maybe around a month.
Used With Halo juice, they last forever for me, I filled a one with prime last Aug and it's still going strong

Tribecca in my current carto has been around 4 months now. If I had to guess, I'd say around 60 to 90 ml thru each carto before cleaning or tossing (for the Halo juices which burn very clean), YMMV.
I do keep them moist with a few drops every couple hours...more If I use one very heavily (tribecca goes really well with cabernet sauvignon

). But also I have a rotation of around 8 to 15 flavors daily....and this changes daily or weekly as well. I have around 30 + flavors I love now, and a few I use when the mood strikes, so prolly not using each individual one too hard. Most often it's a hit or 2 off one, then switch to another and so on...
I also try to avoid letting the carto get hot, so switching it up helps in that dept.