The dev forum has a link to a ROM with better BlueTooth, but not "intended for standalone". Not sure about sensors.
Loki assembled a ROM with working sensors from another Umeox x201 watch.
He has deleted the link when leaving dev.
(Thanks for everything Loki, sorry to see you leave.)
Omate do not have the competence to develop the firmware, they rely on MediaTek, that do not seem to do much better.