I think there were some QA issues with my board.... SMD components are unaligned, also ordered an 8MHz internal oscillator version, but received one with a XTAL soldered. Won't blame for the extra crystal at no cost, but makes me think seller is not checking product.
The biggest problem is board won't work at all. After shorting RST to ground, Optiboot bootloader won't come up. Tried to burn bootloader again using an USBasp, but attiny841 won't respond.
What a pity, really appreciate Spence work on github, but I'm disappointed with this board, think I wasted money.