He's not as good (for this team, at least) as Shaun Hill. Hill will be fine. He's a heady vet with decent arm talent and good accuracy. He also knows the system, having been through camp and preseason as a Ram.
If we brought in Cousins, it would likely be as a backup to Hill, which doesn't really gain us much this year. The only reason you go after him is if you think he's the best option for the future of the Rams QB position, and I can't imagine that's the case.