newB here about to place 1st detail products order, would appreciate y'alls help

[Accumulator]

one of the naming practices that confuses me is the Roman Numerals! what is the difference b/w PI-III & the Finesse It/PI-II lines?

(VERY) Generally speaking, the "III" line is newer than the "II" line. To hear 3M tell it, the PI-III line takes advantage of advances in the field while the FI and PI-II lines are their "older" products.