I've got one on my Stihl FS70. I have a couple herniated discs in my back, so being slightly bent over using a trimmer was always a literal pain. The Darwin grip allows me to stand upright. No more pain.
Mine is a couple years old at this point, and I know they have a newer model - not sure what improvements they've made, though. I like mine, FWIW.
I have Never seen anything like that but am going to buy one. One of the reasons I don’t weed eater much because they are made for short people and I am not short. I end up using it one handed most of the time but that doesn’t work with brush blades.