Switching to t-slot construction makes designing and machining the parts far easier. Also I don't have to worry about the machine racking like I would have had to with the earlier design.
For comparison, here's the old and new designs. The shafts aren't structural, they're a part of the design I haven't put in the new version yet.
The new design is about the same size as the old one, but it's much easier to scale. It doesn't need nearly as many slots as it has. I put in so many since it's easier in Solidworks to pattern the slots like that than only putting a few in. As far as I know, the main difference will be it'll take a little longer to cut it out.