While starwars.com's databank states that crab droids come in a wide variety of sizes, this one is approximate mini-fig scale to the ones seen in the movies.
A very simple creation, with one small custom modification.
This is a very cool and unique lego. Plan to use it in a battle or fight of somekind? If you do, I recomend that you have a swarm of these attacking an elite squad of clone troopers in an Utapau starship hanger.