Duff was an OK pre-season returner when competing against guys who weren't going to make an NFL roster. Moses did a better job returning when he got his chance in the preseason. Some people made a big deal about Duff being Notre Dame's all time leading returner in total yardage, but that isn't very accurate since ND's defense stunk it up while he was there and therefore he also had a lot more kickoff returns than other top ND return men like Tim Brown and Rocket Ismail.
Duff's other problem was that he wasn't going to earn a spot as an NFL cornerback. Duff was an OK college corner in a zone scheme, but he definitely doesn't have the cover abilities to play corner in the NFL. Since the main knock against Moses is that he takes up a spot as a specialist and can't play on offense or defense, Duff's only chance to make the Texans was if he could also make it as a position player.
If Duff is to make an NFL roster, it would be as a special teams guy (but not a returner). As far as his position, he should get looked at as a safety or possibly a third down running back. He just isn't an NFL corner.
