I had one put in. No problems with it being put in. Just slight discomfort. Bled for about 3 months. Then stopped bleeding altogether.
But felt very strange on it. Weird thoughts, unable to cope mentally, unable to think straight. Boobs hurt and felt enourmous most of the time. Put on over a stone in weight.
At one month check up they couldn't find the strings. I was sent for a scan. Took about 4 weeks to get a scan. They can see the coil, it's in the right place.
Due to weird side effects I ask to have it taken out. Dr can't find it. Sent to gynaecologist (another 4 week wait). He can't find it. He books me for another scan at a hospital 30 miles away. I wait another 4 weeks and take a day off work to get there. They see it and book me in for an operation to have it removed.
I have a pre-operative appointment at the hospital, I have another appointment for bloods, then I turn up for my general anaesthetic op. They can't do it that day (despite the fact I've starved, booked childcare, trained a temp for my job, my dh has taken time off work to look after me as I'm not allowed to be left alone after a GA).
EVentually I get it out - after something like 10 medical appointments, numerous days off work and a whole load of hassle.
Unless you really need this thing, I would say steer well clear.