Are you sure that $10 includes an extra leg room seat? You usually pay an addtl $10 for speedier security checkin. Then, it's an addtl charge if you want the extra leg room seats. If you get the extra leg room seat, you automatically get the quicker security line.
My dh is 6'4''. He just flew from Boston to San Diego in a regular seat on JB. It would have been an addtl $95 to get the extra leg room seat for him! He said it was fine in the regular seat!!
Some people really don't mind paying extra for more leg room. If I can get it for $35 or less, I get it. But....lately I haven't seen it that cheap.
As far as the quicker security line goes.....as I said, we just flew to San Diego from Boston....two weeks ago. Those with 'expedited security' go to the PreCheck line. Shoes remain on, laptops stay in your bag and your 3-1-1 Baggie stays in your carry on bag. But.....dh got PreCheck at Logan, I didn't. He just got lucky when doing online checkin....didn't pay more or do anything to get it. I went thru the regular line. I was done and waiting for him....he hadn't even gone thru the scanner yet. So, sometimes it takes longer to do PreCheck! But, it's nice to not have to take stuff off and leave stuff in your bag.