Might be too late for the OP, but for anyone else interested...
We flew BUF <-> MCO the week before last (just before Ontario March Break). Bought EBCI for the following reasons:
1. We'd never flown Southwest, so had no direct experience with their boarding process.
2. It's a busy travel time, and I assumed the flight would be full of other families with young children, all of whom would want to sit together.
3. Even after paying $100 for round-trip EBCI for my family of four, the total cost was still half of what we would have paid to fly from Ottawa or Montreal, and 65% of the best flights I could find on JetBlue.
4. My two kids both prefer to sit with me. If one had to sit with Dad there would probably be a protest, and the idea of sitting alone would likely bring on hysterics.
I did buy our tickets quite a while in advance, shortly after the booking window opened. We had boarding positions A16-19 in both directions. It looked like these were the earliest generally assigned positions; A1-15 appear to be reserved for certain (higher) fare classes and/or very frequent fliers.
What I learned from this:
1. EBCI works exactly as advertised, at least in my experience (I'd seen some complaints in online forums suggesting otherwise).
2. If you just want to be sure you'll have seats with your kids, but don't particularly care where those seats are, EBCI is probably not strictly necessary even at busy family travel times, as long as you will be able to check in at or near the 24 hour mark.
It was nice not to have to worry about it, and to be able to get off the plane quickly since we were sitting near the front. But I probably won't bother next time, particularly for the outbound flight. I have never paid for advance seat selection on other airlines; I'm used to checking in at the 24h mark for best seat selection, and have never had issues with availability (except on Air Canada, but that's a different story). If you're going to be on a cruise the day before your return flight, or anticipate being out at a park and just don't want to have to worry about it, then EBCI is probably worthwhile on the return flight.
The only hiccup we saw with Southwest's boarding was on the (completely full) outbound flight. They ended up short a seat. The flight attendants seemed to be assuming that someone must have brought on a lap-baby and then helped themselves to a seat for that child. Since they take your boarding passes on entrance, there wouldn't be any easy way to identify lap infants. Eventually they found a place to put the "extra" passenger, but I'm not sure where. Maybe a crew seat? They sorted it out, anyway.
lol just an FYI for any future trips
