I have one
They are very effective. It is very, very rare for this form of contraception to fail - when this does happen, it is usually because the coil has come out of place but you can check that the device is still in place by feeling the strings that hang down out of your cervix into your vagina - but don't worry your OH won't be able to feel these when you have sex... The most common reason people opt for this form of contraception is that you don't need to take a pill every day or use condoms, it lasts for 5 years, there are no hormones used and your fertility returns to normal as soon as you have the device removed.
If fitted by the right person you will hardly feel them being put in, either! (especially as you have had a child already - this means that the process is less likely to be uncomfortable). It takes all of about 5 minutes to be fitted, but there is usually a waiting list so if you want one I would put your name down now...
The main side effects of having a coil are increased period symptoms (longer, heavier bleeding, PMT and tummy cramps) but these do not affect everyone who has the coil. I have had no negative side effects except for a heavier period.... There is a very (VERY) small risk of perforation - where the device goes through the wall of the uterus, but this usually occurs at insertion when the practitioner is very inexperienced and poor at their job! The other risk is expulsion - where the device comes out basically - but like I say these risk are very rare and hardly ever occur - you should be aware of them, though.
If you do decide that the coil is for you, I would strongly recommend going to an IUD clinic to get it fitted - because the doctors who fit them there are very experienced and very good at what they do - they fit them every day and know what they are doing. I've heard a lot of horror stories from friends and relatives who have had them done by their GP and it's hurt a lot and ended up getting infected!
I have had an entirely positive experience of having a coil - I hope you have the same!