i was once looking for a quote for 300k united and got no where near UR for that amount.
300K is less worth than 100K united IMO.
Most united redemption's range between 100K-140K, so an account that size is very reasonable, and is not risky, being that you're only redeeming for one ticket. 300K, they'll have to redeem for 2-3 tickets, which can result in red-flagging the account.
Vs. UR that can be transferred or topped off to different account, the bigger the account is the more it's valuable