BuildMaster deployments vs. Rails Migration

How does BuildMaster compare to the Rails Migration concept?

First and foremost, it's not a "competing" process, but more of a complimentary one. That is, BuildMaster can be used to automate a RoR deployment via the RAKE action.

If you're using db:migrate, this is handled via the RAKE action in the exact same manner. If you'd like to try more advanced database development (as RoR's database support does not use features such as triggers or foreign key constraints), then BuildMaster's change script feature is available for you to try.

The primary benefits to doing this are the added dimensions/concepts of applications, releases, builds, promotions, etc. - instead of just files and (possibly) changesets. For small, part-time hobby projects, these benefits are akin to the benefits added by source control and/or issue tracking - just about beneficial enough to use, but not enough to pay for (thus why we have the free edition.)