Is that he's more of what we have already. Rams have two CBs who have some decent natural coverage ability but can't tackle for <bleep> already in Durant and Forbes. And with Alexander he's generally disinterested in it since he can't stay healthy to begin with.
Have to admit it's not like I watch a ton of GB games or anything. Overall though I'd say Alexander is better than Durant or Forbes in his coverage ability. He would help us. But I imagine he is going to have suitors on the market and once you bring him in how much of an upgrade is he over Durant.
So my guess is the Rams don't win the Alexander sweepstakes. That will be another team who is more desperate for a coverage element.