1. No reason to avoid these flights.
2. Any ticket purchased on United.com has their flex booking policy regardless of who operates the flights.

Now having said that, do you have ANY UA flights on the itinerary you're trying to purchase? I don't think UA will ticket it if you don't. So you may be getting to the payment page but once you click "purchase" you will get an error because UA will reject it. Otherwise, if it does ticket then you have 24 hours to cancel without penalty. Might be worth trying to see if it will even ticket?

-RM