since we have the recommendation of 'never entering a password on a website, unless it's the password field of the according website', i'd suggest to build an send by mail request form.

if you enter your email, you can choose to get those first 5 chars of all pwned password hashes to the entered email.
with this, you ensure, that only the pwned email addresses get their pwnge data... (which ofc won't help if the mail account itself has already been hijacked)

this would help greatly, to check wich password may be leaked and need a change.