MK outlets primarily sell factory quality bags. The leather quality is typically lower IMO. The designs are often similar to current or slightly different versions of bags that were in boutiques from previous seasons. Prices are similar to boutique prices but there is usually a % off on most bags.
I've seen MMK (not MK collection) boutique deletes periodically but not often. Boutiques run sales every month cycling out older inventory; the sales are usually 30% to 50% off MSRP.