I do not see any billing concern thus far. However, I do note that Verizon just add $10 per month without changing speeds to 50/25. In other words, the bill still show old speeds, but bill you $10 more than before.
It appears to me that there is no way to downgrade back to old speeds at old price. At least we do not see any mention of it such as if you are not satisfy with the upgrade, we will be glad to restore your old speeds with old price.
Furthermore, there is no router sent for this speeds upgrade.
To sum up, I believe Verizon is doing everything they can to have everyone get onto one of current speed tires and pay as close as possible to current prices without losing customer.