The purchase page uses SSL. The little window that pops up (which is Stripe behind the scenes) also uses SSL.
We used to accept PayPal, though many customers were upset when PayPal would freeze their payment for a day or two. Then we started getting many fraudulent purchases, and PayPal charges us $20 for each one. After multiple hundreds of dollars in these fees, we will not accept PayPal again. They are a nasty company, both for the buyer and the seller. Accepting credit cards still has the risk of fraudulent purchases and the $20 chargeback fee, however Stripe takes measures to reduce the number of fraudulent transactions allowed. We get maybe 2 per year instead of 25+ with PayPal.