We (me, Mrs. Meathead, and Little Meathead) completed our first BE round-trip yesterday. On the outbound, paid $22 to pre-book two seats on the outbound, plus $30 to check one bag, and we were allowed to preboard by the GA (Little Meathead is 6 months old), so it would appear that the GAs have some discretion on that (when I called reservations a few months ago to ask, they said we wouldn't be able to preboard). On the inbound, we paid $49 total to book the A and C seats towards the back of the 788 that don't have a middle seat, plus $30 to check one bag. We more or less boarded at final boarding, so I couldn't say if we would have been able to preboard or not.
The BE round-trip was about $100 cheaper than the next highest restricted fare, and we have no status that would have allowed us to check a bag for free or pre-reserve the seats we got on the return for free, so we still came out ahead.. The travel experience was largely the same as traveling on a restricted ticket: Still got PreCheck, same inflight service, etc., etc. None of the nickel-and-diming you see on ULCCs.