Hey Francis,
you probably mean that G53 fails silently if G53 is used while G91 is active. However the g-code standard defines no standard behaviour for this case. It simply implies that you never use G53 while G91 is active. It would be good style if a CNC controller emits an error if G53 is used while G91 is active, which the Buildbotics/Onefinity doesn’t.
Anyway I believe that the forum users will appreciate your experience with the alternative controller.
Considering that the Onefinity and the Buildbotics contain much more than the CNC Controller, but also the four stepper drivers and a power supply, I always found that it is not expensive. The Onefinity CNC Controller when sold as a bundle is much cheaper than $500 (subtract the “black box option” when ordering an Original or PRO Series, and you see the real price difference).