I am about to buy some Marathon Plus for my 27.5"...........mainly as they are one of the few slimmer/slicker tyres that will fit.
Good points...........they are virtually bomb proof ..........see link below
View: https://www.youtube.com/watch?v=Uz8fT13rtlk
Bad points...........they are supposed to be extremely difficult to fit............see link below.
View: https://www.youtube.com/watch?v=ymvOLOJUVs4
My feelings.......................
a) hopefully I will not get a road-side puncture so that problem won't arise

b) my LBS is going to fit them f.o.c.
c) they appear to be a lot slicker than my 27.5" x 2.1" Rocket Ron's they will be replacing..........and make my cycling easier