I suggest you read the FAQs and Pocket Manifesto. It's not a purely economic proposition. Not all cryptos are PoW. And, like compound interest, things accrue over time. Lastly, it depends on your future view of where crypto is going versus the US dollar. In some ways the Pocket Miner can be thought of as a device for converting US dollars to crypto in a friendly way; do that conversion now (and over time) and perhaps benefit later? It depends on your view of where crypto is going.