Aren't they complementary? Aztec allows BUYING Bitcoin using vouchers you get from retail stores.

Bitrefill allows SELLING Bitcoin for vouchers you can use at retail stores in exchange for goods

At least that's how I remember them… 

 they seem to have extended it to gift cards/vouchers also, but for sure i've never been in any part of the world where they are in use (been mainly in EU, UK and former yugoslavia) 

 ah yeah, just following it, it's only for trading to other vouchers, like offgamers, where you can use them to get steam and other game platform gift cards