I've got friends that use them. Typically some cash, their DL and a credit card is all they clip together. No extras.
I only keep my wallet in my back pocket when I am out; at home its on the dresser and in the office in a drawer. In the car it goes in the door pocket for easy access.

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95 E300D working out the kinks
77 300D, 227k, station car
83 300CD 370k, gone away
89 190E 2.6- 335k, no more
79 VW FI Bus- 145k miles, summer driver
59 VW Beetle ragtop- 175k miles
12 VW Jetta- 160k miles