I am not sure if there is any functional difference other than the refills and the PRO being available in fashion colors.

If you are considering purchasing a Zeno and the Pro is less expensive up front (less cartridges) then I’d go that route. Mine was pricey $200 but it’s been the best $200 I’ve ever spent in my life. My skin looks great and I’m able to zap the pimple before it has a chance to develop into an ugly mess on my face.
And you probably already know this the Zeno alone isn’t going to solve the acne problem you need to be religious about your skin care regimen. My skin care rountine is here if you are interested.