I have had a 2018 Stumpy Carbon 29er for a month and have used it considerably in that time.
I wanted a more capable companion for riding than my skittish carbon racy 29er HT which I love, but as a recent returner I wanted another bike for long days in the mountains that didn’t smash you to pieces,and also a bike for getting to the local trail centre to improve crap technical ability.
It has been a great acquisition, it can climb, gives a snappyness and quick pick-up that you don’t get from alu (that always feels a tad leaden!). I ride it for hours and still love it afterwards.
The black bit is a storage bit for a 29er tube and co2 tools etc. Very handy feature