Using regular expression match instead of prefix, is there a way to add a difficulty and probability check? Seems to only report keys/s and total keys tested.
Assuming the output is random:
How many randomly generated texts (in the base58 dictionary that *coin addresses use) are going to match my regex?
The output is not exactly random, so that's a shame, but it will give you a good enough indication.
Remember they call it vanity addresses for a good reason! It's all kind of vain.