You can't compare Alterpay with Paypal. Its miles behind paypal but yet it's something many use as an alternative for Paypal. Specially it comes handy when you are in a country which you can't take money from someone using Paypal. or you can't use Paypal.
Year ago there wasn't many sites which would accept Alertpay as a payment method but there are now. So I was checking about Domain registrars and resellers who accept Alertpay. It seems Directi resellers use Alertpay.