I've flown Delta a lot more than United, and have been bumped dozens of times on Delta, and a few times on United. I echo your inputs.

Simply stated, if you agree to be bumped - have the agent "protect" you on a flight - and if you think you can get first class, then request it on the bump. I've found no problem with Delta confirming first class on another airline if I'm confirmed in frist, but I've had no luck with United. Also, I've had no luck with UAX location in getting $$$ from them instead of a free flight. I've not taken bumps because of this.

I've even had trouble getting first class on United when there were first class seats later on another united flight. They tell me no upgrade seats are available. Well, if they want my first class seat now, they better trade me for one...

Billy