I recently purchased the Reformation Study Bible. As a relatively new Christian that recently concluded that the Reformed teaching is accurate and logical, I wanted to have something I could rely on with notes from a Reformed viewpoint and not something tainted with Pentecostalism, Dispensationalism, or otherwise.
On my smart phone I did download a free KJV Geneva Study Bible from Google Play which is also of help to me.
The only knock I have on the RSB so far is that there is no red-letter text and outside of the maps, everything is black and white. It makes it a bit more difficult for the eyes to pick out a given thing. I also prefer two-column text with notes in the middle as opposed to the one-column of the RSB with notes on the sidebar. As someone who is nearsighted and needs reading glasses on top of contact lenses, I wish the font was larger as well. So my issue is formatting, not note quality.
Although not Reformed, I still use the voluminous Thompson Chain Reference for general topical study and historical understanding. It's a wonderful addition to anyone's Bible study regimen, in my opinion.