Yes, to me Arc’s image definitely shows a collet chuck without flats.
Interestingly, in my copy of Arc’s printed catalogue at least one image of R8 collet chucks shows very definite flats. I wonder why flats ceased being a feature of these chucks. Is the assumption that most users will have some means of locking the spindle?
The APT R8 collet chucks I’ve got in three different sizes have all got flats. Runout measured up the taper of my ER25 and ER32 chucks is about 0.01mm: runout up the taper of their ER40 chuck is an impressive 0.002mm.
The only disappointing things I’ve had from APT were some ER20 “super precision” collets, two out of three of which had more runout than their counterparts in a very cheap set I bought off Amazon for woodturning.