X-Dies stop brass growth with repeated resizing, even on semi-autos like M1s. They are a FL sizing die that mechanically prevent brass from flowing towards the neck when the case is resized, thus eliminating brass growth completely after a couple of thou initial increase after your second firing. Many experienced reloaders swear by them.
The idea is to NEVER trim more than the initial trim over the life of the case, not just occasionally when it needs it.
Therefore you never have to measure cases again either, use them confidently till they fail, if ever.
Use the X-Die in conjunction with a form/trim die, Lee bullet seating and factory crimp dies, Lee powder dippers, a simple balance beam scale, and mild loads, and you have the simplest and easiest of all reloading time saving processes. For beginners or experienced reloaders, this can be a Godsend.