In some way it may not be so bad if there was sufficiant gate staff in the gate orgainzing the boarding, and ensuring correct people board at the right time.
I think the worst thing with free seat boarding is on a airbridge
Everone tries to pile straight into the first 4 rows blocking up the aisle on causing queing up the bridge and a slower boarding.
Funny thing is after boarding everone is cramped in to the fisrst section of the cabin, yet the pax who went to the back are nicely spread out with plenty of room.