I believe there are two types of I-Line covers.
One style is a one piece cover that has a door. (Like a regular QO Panel
The other style is four (4) pieces; one for each side, and one for the top and bottom.
Ate front of the breakers are "exposed"; but NO live parts are exposed.
As to the I-Line blanks; if you have the factory (Sq D) parts; they are approved as "blanks; to cover spaces that no branch cb's are installed in"
The parts are all UL listed for there specific usage. Make sure you install the screws that mount the blanks into the panel.
If there is major concern about the plastic blanks, you could suggest that "spare" I-Line cb's are installed, but thats $$$