I noticed that the seat back pivots freely on the cushion and does not lock into an upright position or lock into a recline mode when the recline feature is activated. Is this safe?

The Oobr booster seat is designed with a free pivoting back in order that it fits different vehicle seat angles so that the back of the booster seat will always be in contact with the vehicle seat back. Oobr was designed such that this free-pivoting back can be used in conjunction with Oobr's rigid UAS system to provide a controlled maximum recline position. The UAS system operates like the seat track on your driver's seat (slides fore aft) locking in different positions — this is what locks the booster seat relative to the vehicle seat while the seat belt secures the child in the booster seat relative to the vehicle seat. Providing the booster seat's lower UAS connectors and the booster seat back or headrest is in contact with the front surface of the vehicle seat back or headrest, that recline position is safe for use.

NEVER use the recline feature without the booster seat's lower UAS connectors securely attached to the vehicle's lower UAS anchors. When using the booster seat without using the latch connectors, the back of this booster seat base MUST contact the vehicle seat back.