I wanted to mention something.....
It was either last fall, or the fall before - I got the EBCI for myself, but not my son, I figured there's only 2 of us, I would just hold his seat (yeah, yeah... shame-shame

)
I ended up deciding a few days before we flew, I wasn't even going to mess around because our flight was super early, and I didn't feel like waking up at 6am, just to check him in. I then purchased his EBCI, as well. $10 was worth me not waking up, early.
Keeping in mind, I had purchased *MY* EBCI months and months earlier, and his was purchased just days earlier - and *his* check in number was ...heck ...like 10 or 15 numbers before mine.
So.... he got on, and.... saved my seat. An exit row seat, at that. It was the first time flying at age 15, and we FINALLY could sit in the roomy row.
I don't get the rhyme or reason with their assignment of the EBCI numbers.
However, that being said - one of us is always the next person after the business dudes. I think it's worth it.