This is a recurring theme on these boards, whether to buy an off brand lens, battery, etc. Some say... rubbish, get the OEM, others tout their excellent experience with a given off-brand. I think a lot of it has to do with one's overall view of their photography. Clearly someone whose income depends on one's camera will probably buy OEM batteries and lenses. There are a few folks out there who seem to glory in the "deal" and love to boast of their "bargains." If the only 10-18mm full frame lens in the marketplace is an "off brand" and one needs/wants that focal length, there's no choice. Some just prefer Zeiss or other brands. Otherwise one is parsing value for money.
For my A7RIII, I have almost all Sony lenses, a friend, whose work is excellent has only Zeiss and Voightlander's. I used a few off brand batteries in my Fuji's but am now sure why. When amortized over the life of the gear, the difference is pretty trivial. There was even a discussion, I believe on Fred Miranda, about whether the owner of a new A7RIII even needs a second battery! Seems a bit silly to me, but to each his own.
