We like the looks and efficiency of the Tailgator too, but opted for the REI Alcove because, to us, it is more versatile. We like the idea of being able to place it wherever we want in relation to our 550, and we can also use it in other situations. (i.e. as a shade shelter at the beach, or as a shade over our grandbabies kiddy pool in the backyard.)
We will report in once we use it in the field, hopefully within the next month.
No side walls for us, at this time.