Difference between Meridian Pro from Market and PayPal

First of all, buying Meridian Pro from Market or PayPal does not differ in the application features. They are totally identical except the authorizing method. Also, you don't need both of them. One of them is fine.

The differences are:

• With a Market auth app you need to keep it installed in the phone, and with a PayPal auth key you need to input it into Meridian main app.
• Market auth app is Google account dependent, where PayPal auth key is device dependent.
• Thus, if you changed your phone with a PayPal auth key, you need to mail me for a new key.
• In the other hand, if you changed your Google account for some reason, you need to rebuy Pro if you're using a Market auth app.
• With price $2.99, PayPal's fee is $0.42 and Market's fee is $0.90. More than twice, but since on PayPal I need to pay effort for device changing request, both are fine for me.

As a user I'll suggest you to buy from Market if you can. It's much convenient.
I have also heard PayPal will join Market's payment, maybe it will be the time I totally shift to Market buying.