mekanism genuinely is a shit mod though. for some brilliant reason, your "personal chests/barrels" don't actually prevent others from opening them unless you have a security desk placed down. and you have to actually set them to private, too. but you can also set things to "trusted" mode which is just like. a single list of players. that applies globally to all your machines, I'm pretty sure. you can't set a specific player for a specific whatever.
it's almost anti-collaborative, in a way. if you want to have, say, a money safe which only you and your company can use, that's all well and good. if you need some privacy for a solo thing, that's all well and good too. but if you want something that only you and someone outside your company can use? tough shit.
I actually don't know, I don't use any of this because mekanism is a shit mod, but this is how I understand it to be, and I understand that it's a system lacking in "being good," for lack of a better word. multiple trusted groups would work. the way rftools does it is good minus the fact that you need to add yourself to the list (this led to a really fun problem with back in the day, but I digress).
moral of the story is I will never stop shitting on mekanism. WIFESEX OUT!