I use CO2, although I hardly ever need it with tubeless for some reason in the U.K. The only time I’ve needed a pump regularly since going tubeless was riding in the desert in Arizona where the extraordinary cacti thorns everywhere routinely punctured the tyres. Being 15yrs ago, ‘Slime’ plus a quick pump after it had congealed (like something from the Dark Side) was what the locals showed us was best.
Hypocritically, I do also carry a little pump as well, but I don’t know why I do that and, having never used this one, I can’t really recommend it to you ?