Very safe! In fact much safer than emailing or chatting sessions (never do this) or even calling in a order to various stores or websites.
Never email or use chat features for your info, it is open for anyone to see while in transit and can be stored on many servers across the world forever. Don't use email or chat!
Likewise if you are calling a store or web concern and telling them your card info, remember the person you are chatting with usually writes down your info. Your info at that stage is subject to the honesty of whoever is handling it and it may get passed on paper wise to others inadvertently. Not a good idea.
Both of the above reasons are partially why we only use online purchasing for those using credit cards. As such, no one here or elsewhere except the card processor ever sees your info. The connection is private and secure and our website use SSL for security and have other compliance measures.
We have actually seen in today's world, many websites including some popular ham radio sites using old version cart software and other non compliant software. We don't do that here, your info is safe.