I will investigate blade thickness on Monday as I will pick up some Fessy-stuff anyway and will be able to cross compare in shop and with a caliper.
I do believe that the blades are actually thinner than the standard plunge saw blades (as the Mafell ones are) and hence the crossed out compatibility symbol. I think that using thinner blades that aren't compatible with the existing machines is a problem for the end user - blades are not cheap and buying a spare blade would be a more complicated matter - especially if they are not cross compatible.
Unless any moderators or other members can chime in on the matter I will post back on Monday afternoon (CET).
Snippet from the manual:
"Only saw blades with the following specifications can be used: saw blade diameter 160 mm; recommended cutting width 1,8 mm, max. 2.2 mm with restricted function of guide wedge; locating bore 20 mm; recommended steel blade thickness 1,5 mm, max. 1.8 mm."
See my underscore: this might imply that the guide wedge is around 1,8mm?
See last paragraph: This implies that the blades are 1,5 to 1,8mm thick, i.e. slimmer than the other plunge saw blades?
I think the main point is lack of compatibility with the other battery operated saw - for the TSC55 the HKC blades are not an option and for the HKC the TSC55 blades are not recommended. I think this is a serious flaw as they would complement each other more of they shared blades.