I don't know the particular model but have D4, Alpha and Alpha II pieces and find they are pretty comparable in quality.

I think the D4 line designs are typically a couple of generations old so you may miss newer features (e.g., different size laptop sleeves, etc.)

You've highlighted some of the big differences but missed one of the most notable. The outlet stuff usually has a leather strip running across it it, which looks quite nice but highlights it as an outlet item (if that is important to you). The features in the D4 inside the pockets are typically a bit different -- but IMHO no less in utility.

I wouldnt hesitate to buy outlet but most of my Tumi stuff is regular retail, bought strategically when Tumi runs their 20% off sale, and then purchased from a retailer where cash back was available or they had a promotion running where I could get a further discount (e.g., Amazon has had 20% off select item promotions that aligned with Tumi's sale).

Good luck.