I have the M18 string trimmer, I use it all the time.
With 3 8AH batteries I can do 2x600 feet of driveway with tall grass and using a .095 line
The self feeding head is great, cut 20' of line, feed it through and turn the head to load.
I do a few thousand feet of tall grass and weeds every few weeks, so far it's only overheated once, yesterday, but it was 93 and humid and I was running ti straight for over an hour.
I have the M12 impact and drill/driver and use them all the time. THe stubby M12 impact is pretty tough and I have not thought about getting the bigger M28 one. It is light and takes a while sometimes to break the wheel lugs, but it does.
I now have the M28 inflator, which I think I have used 20 times already around the yard and I have had it a week or so. It is kinda weird on the gauge, but it is fast enough to blow up a flat lawntractor tire without having to jack it up and strap it. Works well on the larger truck and tractor tires and does not weigh much.
I also have one of the M18 lights for working in the garage while redoing the electrical. Lights up the 2bay plus garage really well.
The M18 head works well, but not quite as happy with the pole saw, a little too slow and does not oil well enough. Usable, and I have trimmed hundreds of tall thick bushes, but will probably buy a gas one in the future.
I have not had a single battery failure on the M12 which i have had for about 8 years, or the M18s which I have only had for about 2 years. I buy the batteries usually when they have a tool with free battery or some other kind of sale.