I have been using one for over 10 years now (well, 2 actually, since they wear out after a while).
Marvellous thing - wouldn't be without it. Had it when an old-style copper coil led to increased bleeding. The Mirena has given me 10 years of miraculously light menstruation. Anyone with experience of 3 week long heavy flooding will appreciate my delight!
Re the hormones, I think you need to exercise a sense of perspective about it.
I have always been incredibly sensitive to synthetic hormones (pill, mini pill, progesterone tabs, etc) but those are HUGE doses compared with the Mirena.
The Mirena is designed to last for 3-5 years, and is the size of half a match. It contains TINY amounts of hormone, which are released very slowly over that time.
There really is no comparison. synthetic hormone by pill can feel like being run over by a steam roller.
My experience was that (having had 3 coils fitted by 3 different people) the comfort level of the fitting and for months afterwards depends ENTIRELY on the skill of the fitter. One left me shocked for hours, and spasmy for weeks. I was at the point of having it ripped out when it suddenly settled down. Another left me with a strange pinched feeling on one side, but again settled down (I think it was inserted lopsided). The third, fitted by a gloriously no-nonsense Asian lady consultant still practicing in her 80s, was so quick, gentle and efficient that I didn't feel it at all, either during or after.
I kind of think that most of the time when people have problems with coils it is the hamfisted fitting technique, not the coil itself! If they shove it in at an angle, or up one of the sides of the womb, it will never get straightened out. And of course finding a good fitter is simply the luck of the draw.