This is a new product review from the FSRH. Levosert is an LNG-IUS, which is the same as Mirena.
It seems to be as effective as Mirena and to have similar side-effects.
The major downside is that it only lasts 3 years (though as more data becomes available this may extend to 5 years).
It costs £66, so is cheaper than Mirena at £88, though cost per year is more at present.
Another disadvantage is that it can not be used for endometrial protection with HRT.
Remember that Jaydess, another LNG-IUS is also available.