I agree with zac, it's great as a going out bag, or going in bag when you don't want to haul in everything - like to the store! It fits nicely in your bbag!
practicality wise I chose mini coinpurse because it is smaller and thus fits into any sized purse or most pockets even! But both are necessary pieces!!! I can't wait to get my first m/u one of these days!
I don't have any m/u clutches, although I'd think that in terms of size it would be more practical than a mini coin. I do, however, LOVE my mini coin purses because for something that size they sure do hold a lot...
It depends on what you will use it for. I have two coin purses and they are really great size but it could only hold a few lipstick or lip gloss, powder, sample perfume. I think make-up is more practical.
I use my Mini Coin a lot more than my Makeup because it fits in my clutches and in my Firsts. The Makeup is a great organiser for a bigger bag, but the more I carry my small ones, the more I appreciate the Mini Coin. I actually plan to buy another one in the near future.
I've wondered what most people use.
I think they each serve their own purpose but it really depends on the size of your bag. I use my coin purse every day...