There is no problem to uninstall swirly and install again, even to totally make a full restore of your phone is no problem. You will get the same license as long as you use the same phone.
I would say the payment is as save as it can get. PayPal is The player when it comes to internet payments. Please feel free to look around at paypals site (http://www.paypal.com
) to see what they have to say about it. For example when it comes to paying with creditcard at paypal. They handles all that stuff. We as the seller never sees anything like creditcard numbers etc.