I like Demps and I think Madison will be a decent enough stop-gap at CB until a younger player develops or they can sign a better free agent in a year or 2. McQuarters is also a decent signing, unless he is forced to start most of the season, in which case CB will remain a weakness for the Giants. I don't know much about the other guys. They seem like deep depth and special teams players, but at least they are all young, so hopefully they have some upside. I don't think any of these signings should stop Accorsi from drafting a good CB on the first day of the draft. I would like them to concentrate on DT and OLB first, though, and I think obtaining this depth at least gives them that option.
Jason Bell is an excellent gunner on punt returns and above average special teams player (non-returner). As a CB, in the three or four years with the Texans he has never been higher than the 4th corner when everyone is healthy and normally like 5th or 6th. Career special teamer; horrible defender.