The link leads to an error 404.

You can use a prepaid visa to buy account credits

Have you tried doing specifically that and/or do they claim you can do specifically that? I tried doing the same thing when making a Tuta account and it wouldn't accept prepaid cards, though they do have a 3rd party source you can pay cash or Monero for gift card codes, giving true anonymity

but it's not the biggest hassle to convert from monero to bitcoin for a purchase.

I think the issue is that Bitcoin hasn't been anonymous for a few years now (unlike Monero).