I think Big Rigidbot and Mankati Fullscale XT Plus are two different directions,
Big Rigidbot was designed with many refit / DIY tendency, details like total open frame, many 3D printed parts, optional functions...
It is suitable for those who like refit device and spend times on the device, try many possibilities about the device, not just buy it for 3D printing.
Mankati Fullscale XT Plus was designed for one purpose: stable and reliable 3D printing,
details like one-piece solid steel printer body, gear motor feeder, no 3D printed parts, E3D V6 hot end...
I think it is much suitable for experienced users who have clear and specific purposes.