I am already a heavy user of SERPWATCH. To be honest, I am not sure how both compare for many things but I do like the extra features provided by SCREPY and there is definitely room for both (hint the Briefcase deal is very generous).
As of now, I am not using Screpy for Keywords rankings, but what I get is more than enough. A lot of things to look at with detailed explanations on how to fix them to keep your website "healthy".