The RTC with battery atached is not working on R5C. In this link is explained possible causes...
forum.radxa.com/t/hi-has-anyone-run-into-rtc-trouble-with-rock-3a/8522

The RTC clock is rewrited from rockchipp clock in boot process.
Please,... release a version kernel properly compiled to use the battery with the RTC or a guide to do oneself easy way.

The computer R5C is very good and works very well with Debian desktop.

The bluetooth don't connect very well and is something related driver because to change the adapter, then the connection works without problems.

Good little computer.