Yes, Kakashi covers his implanted eye because he can't switch his sharingan on and off as it's not his natural eye. They took it out of Obito while it was active so that Kakashi could use it that way. Danzo, I would assume, is exactly the same. However, we have not seen Danzo with a Mangekyo Sharingan, only a regular. Could he have one? Sure, we don't know though.
We also know that each individual person with a Mangekyo Sharingan has their own individual talents with it. Itachi would invade your mind and use, pretty much, the ultimate hypnosis. Kakashi send whatever he hits into an alternate dimension. It looks like Sasuke has a ridiculous amount of control over his amaratsu as he's the only one known to be able to remove the flames after they form. Madara is an unknown.
i agree to all what you say about kakashi lack of turning on and off his sharingan.
Danzo...i dont thinkt he ahs one, he has actitude to kill anyone for hsi own benefit, probalby a friend, ect.
Madara M.sharingan skills have to eb connected with his so long life span, i mean he fought the 1st hokage long long ago, and he looks very skillfull for his age, he should be very old like more than 100 years old, so probably he use M.sharingan to chnage to another body as orochimaru or somehting like Kakusu (the imortal akatsuki member with many hearts and patner of Hidan), well that is what i think.
Kashi got his M.sharingan wehn obito died (amazing gift).
and ther eis one more thign that i woudl liek to bring up, is about Naruto, we knwo the skills of teeletransportation of his father, shown in kakashi gaiden, why naruto cant use that yet? isnt suppose to be some blood line ability?