Test prints on MakerGear M3 (black filament) vs. Monoprice Select Mini 3D Printer V2 (white filament).
The M3 did significantly better. Still dialing in the Mini 3D; in this print the top layer was consistently too thin across all parts, all sections of the bed. Not sure if this is an issue with my Simplify 3D settings, an alignment issue(s), or what. M3 was sliced with default Cura settings through Octoprint with default print quality settings.
The design itself is adequate, but for my purposes will require a remix/extra parts to (a) hold down the channel, (b) stabilize the rack, and (c) add a servo mounting bracket on the other side. More or less a complete rework, but for some purposes, what's here is likely ok.
10% on M3, 20% on Mini 3D