My AN8008 is working fine after I used PPE contact cleaner (DeOxit) on the rotary switch. Before it was awful, high (zero) ohms readings, power cutting in and out. It's the crappy copper wipers oxidizing. I'd used oil, grease, teflon lube etc. but nothing lasted. Now it's around 0.15 ohms leads shorted in ohms-mode and consistent, reliable.
The little 8-bit MCU it's written in assembly language and minimal OTP or mask ROM memory, so I wouldn't expect the feature really needed- NULL or ZERO.
For the Q1, as always gold is expensive but necessary on signal relays. Hongfa HFD2/003-M-L2-D relay, "D" option is Ag+gold plated contacts, latching 3V coil.
So I'd expect gold on both sides and a bit of sealing, should beat a cheap rotary switch?
What I don't like about latching relays in multimeters is any bump knocks them to the other latching position, which can be a mess.