"All ten of the TV episodes ("mini films") are included in the Arrow set. Missing are the alternate edits of the two TV episodes (V and VI) which were selected to be released theatrically as standalone films ("A Short Film About Killing" and "A Short Film About Love"). Of course when the Dekalog was shown theatrically worldwide, parts V and VI were included - only this time just as they were shown on TV. The rights for the longer standalone film versions belong to another distributor in the UK.
What the Arrow set has over the Criterion is bitrate (2 per disc vs 5), framerate (native 25fps vs 24fps with 4% slowdown), slightly more picture information (the caps show more on the left and right), early Kieślowski films (Pedestrian Subway, First Love, Personnel, The Calm, Short Working Day), documentaries about Kieślowski/Dekalog (Still Alive [2007], Dekalog: An Appreciation, KKTV), 128 page book, and price.
(It looks like both have "1990 audio recording from the National Film Theatre in London" but the Criterion has a number of interviews that might be exclusive, as well as its own booklet)."