I have all the old Roman sets and all the round shields are definitely painted, not stickered. 6491 is part of the new line so it may be different in some way - possibly stickered, or possibly with a different handle like they changed the handle on the scutum (rectangular shield) for the new series.
Regarding historicity, the Romans did have round shields. There's some contradictions in the naming: I've seen clipeus and parma (or parmula) used to refer to round shields. Clipeus and cetratus are also used to refer to the oval shields. I haven't sorted out which is right yet.
The scutum was dropped in the Late Empire and the rank and file all went to the round shield. There's some famous imagery in a codex called the Notitia Dignitatum that displays the wide variety of shield decorations, including what looks like the first yin yang symbol in the world! Point being that if you're doing a late period unit the round shield will be appropriate.
They are wrong about the spear. During the period that their theme represents (ca. 100 A.D.) officers would not be carrying long spears into combat. The new Roman series is full of inaccuracies like this.