I am on my second set of Costco RV/Marine batteries (yes I know you asked about WalMart). My first set lasted 6 years. Nothing wrong with them IMO. Now obviously Costco doesn't manufacture batteries, they buy them with the "Kirkland" sticker put on them, and some big player makes the batteries for them.
Point is, yes, you can buy AGM ones for $300 a piece (the price for the "good ones" at a local battery retailer) that will be better specs wise, and maybe last 10 years, but my $50 a pop Costco ones have served me well - lasting 6 years. If these G27s last like my 2 previous G24s did, I'll be very happy with them.