[@Mr.Dave] Sorry for the double post, not sure how that happens. I have another update:
I sent an email in reply to the email from them when they confirmed my previous order. I included a screen shot of my antivirus telling me they were using the wrong security certificate on their site. They told me it was a false positive — well, the certificate is correct or it isn’t, my AV says it isn’t.
They reset my password and gave me a link to a different login page. I was able to change my password from within my account once I was logged in. Got a few odd errors, like a 404 Page does not exist, and an “Insufficient privilege” or something like that, but it eventually all worked. I get the sense this is a fairly new company and they’re still trying to figure out what they are doing with their web pages.
So, it at least seems possible to use their site without getting antivirus warnings. I may still try out the Vector Graphics Club offer.