I am scheduled on a UA codeshare with Swiss for Zurich/SFO for my return leg from a Europe trip.

My understanding is that despite Platinum or 1K UA status, I cannot select seats ahead of time and I am unsure of upgrade avenues.

What has people's experience been with UA/Swiss codeshare? Is it worthwhile for me to add a few hours onto my drip to take a flight with a connection on a true United flight?

Thanks!