I sprung for the $10 membership on the day they started requiring it. At the same time, I bought 3 $50 gift cards, so saved $4.50, $5.50 to go. Since then, I have made three purchases of 2 $100 gift cards (about $4 savings each), paying for the membership and then some. However, this was not without issue. The first time I went to order $100 gift cards, it would not allow me to add them to the cart, but just gave a generic error message and no reason. An incognito window fixed this. I added them to my cart, then logged in and checked out. The next time, I ordered with no issues. Today, I placed my 3rd order of $100 cards and had to use incognito again.
I don't know if the times I've had to use incognito are because the website is garbage, or because I'm not supposed to order cards so close together. However, I've definitely been able to get my money's worth out of the membership, and hopefully I will be able to continue buying the cards all summer to pay for our fall trip. 4% savings on an expensive Disney trip really adds up.