The outlets still offer a number of Generation 4 pieces, which are now a couple of generations behind but the differences are not huge. If the Tumi logo on an Alpha is a silver oval it's a Gen 4/outlet piece, if it's a black rectangle it is a current model. The other main difference is that the Gen 4 does not have a monogram patch. It seems to me that the color of the current models is a bit more of a jet black, but that could just be my eye.

There are also lining and pocket differences and tiny feature distinctions here and there, but in the main if you just want a bag to use there is no reason not to go with the Gen 4 unless you must have the latest model.