I was also woried about the possibility of losing cash but the band (haven't tried the clip version) has held the money in quite well, but I suppose in the UK all our notes are now 'plastic' notes so are a little more robust compared to paper notes. Prior to the ridge i had one of the generic wallets with the pop up cards via a button and a flap for notes attached - see here
wallet it was OK but still a little bulky.
I also tried out the cheaper spigen version of the ridge - really not worth the money as the elastic broke within a few weeks but it at least demoed out the style which I have come to enjoy - if you are unsure you could try a knock off knowing the ridge will be better.
They also do a 'cavity tray' which fits inside the wallet, it's ususally for a random key or some coins BUT you could fit a few folded notes in?!?
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