I recently exchanged £50 into Bitcoin to test out the new crypto features on Revolut. Was a bit disappointed to realise that Revolut automatically exchanges crypto currencies with normal currencies so Revolut automatically exchanged Bitcoin into £ when i tried to make a purchase with my Revolut card, having run out of £ funds.
IMHO, this feature is not appropriate for people who use crypto for investment rather than day to day transactions so I will not be using the crypto feature because of that.
I am sure there are better solutions but perhaps Revolut should allow you to disable the auto exchange between crypto and regular currencies (or enable auto-top up, for my particular case).
PS. I use Revolut for a joint account with wife, which makes control of funds even more important