Like the Mi best of anything I've used solo in the car (solo pun intended!). Two biggest advantages IMO are on demand vapor (so no cooking if you're not hitting) and it being so indiscreet. So far have mostly tested this on long daily commute home, so going lower temp and not needing to reload only a small load. Also very nice to vape up on the way out somewhere in the evening, especially if short on time to get in a good sesh before leaving the house. Seems it would do well on a longer ride and could adjust screen up to accommodate larger load. Issue here may be a desire to stir, and could be kind of tricky behind the wheel with size and form of load in stem. Quick and easy enough at a light, though. Have tried a couple techniques experimenting with a larger load. So far easiest way to mix the load up quickly with no spillage is to dump into hand using a pen cap as a tool to "stir" it out into palm of hand. Then just suck it back up into stem.
I don't really like to leave a load in the stem and stem in MI all day, so use a small jar I have for storage. Medium grind in the jar and 18mm GonG just fits in the top. Hold jar inside loose fist with stem in, suck up some ground and ready to go. One smallish/medium load usually gives me the 8 - 12 nice light tasty hits I'm looking for to chill while on my way.
I don't flaunt it in use, but am not super careful with it like I would probably be with something more "vapey" looking like I feel a mighty or others would be. I just try to use it so it looks more like an e-cig mod to anyone who catches a glance. Easy to do at a light if you stay staggered (not window to window next to anyone in adjacent lanes). After nearly daily use like this for a couple weeks or so have never even got a second look that I've noticed. And, not hard to time it so you get 3-5 second pre-heat and a good 7-10 second hit while moving. Not hard to do it all. Just make sure you pay attention to your hit so you don't accidentally get a cough inducing lung buster!
One issue to be aware of is 18650's out in a hot car. Don't think this will be an issue because Mi itself shouldn't pick up much scent. With the way you load everything in the stem, seems like any vapish smell would be there. So no need to pull battery to carry it away from car. Can drop whole Mi in my messenger bag or lunch bag without worries of smelling like a stoner in the office. Or, can pull the battery quickly and easily and take only it if you prefer.
Think it is even better for this than Zi will be, because of form factor. Certainly better here than solo and some others, for all these reasons. Still like my VapCap some for this too, and is also discrete. But, much more difficult to use, empty and reload than Mi.