I bought the cash clip because I had trouble holding more than a few bills int he band of the wallet before it got to bulky. i know how old fashioned it is to carry cash, but a lot of places offer cash discounts and I like to take advantage of that.
The wallet cash clip just slips into the back of the Ekster Pro wallet with very little problem, is very snug, and now I can hold a good number of bills without compromising the thickness of the wallet. I love it and would recommend this upgrade for anyone who wants to carry some cash with them.