I'll add another data point of strongly preferring it. Check in early so you can board early so you can get a good seat. I'm fairly punctual and this system rewards me for that without needing to open my wallet, so I'm a fan.
That said I agree with the grandparent comment about avoiding them for the foreseeable future based on this fiasco. Hopefully they get it together at some point.
Absolutely love it, choice of window or aisle seat is guaranteed if you’re not obsessed with being the very first person off the plane. Also in practice Southwest’s system is the fastest way to board.
Personally, having flown with them for business for 5 or so years, I generally preferred it to assigned seating.