Comment by CapstanRoller

There are always downsides:

your personal card can get fraud-flagged, which is a huge pain to fix.

It can also get banned by Stripe/Braintree/etc, which will really mess things up until your bank issues you a new card number.

Never use a personal card for testing, maybe with the exception of being the sole proprietor of the business or if it's a hobby project.