Yes and no. If you consider this as a linter there are many others out there. Most of them in my opinion generate too much noise. I think that effectivejava is useful to explore your codebase, run a few queries and find out some facts about your code: how many utils classes do you have? How many methods are taking more than 5 parameters? You can run easily the queries on the whole project or just some packages and correct your aim as you find facts (for example, you may start asking how many methods take more than 5 parameters and realize they are 1000, then you want probably to start focusing on the methods taking more than 10 parameters. Or you can find that some classes with this problem are generated code and you do not want to consider them).

About the usage as a linter it tries to keep rules to a minimum of sensible rules, the ones explained in Effective Java. We chose them because they are rules well understood and accepted by the vast majority of developers so we hope to reduce the number of questionable findings returned to the user.

I'm also curious if this offers things Sonar doesn't.

My thoughts too: Sonar, or Checkstyle+PMD+FindBugs, is already ingrained in many of the larger codebases I've worked with.

Of course this is purely anecdotal since I've only worked with +-30 over the years.