I have the Mirena. The cost, over here, is nothing - as it is a contraceptive, it is free.
I've found it to be great as it has reduced my periods to almost nothing though that did take some time - months rather than weeks.
As I had already had three children the insertion caused only minor discomfort.
The only downside I have had has been acne on my back, (never had that prior to the Mirena) and on my face - not constantly but enough to be annoying.
Despite that, I am reluctant to have it removed - working in an all-male environment it is a relief not to have to deal with periods every month so, it stays.
