Bitcoin Core (BTC) is 'smaller' blocks at around ~4mb with Segregated Witness. Thus there is a limited amount of on-chain txn's that can be added to a block. You then sort of 'bid' for a spot to confirm your transaction, higher fees creating some sort of favoured priority.

You could do your own calculations by looking at the mempool data, cost per byte, then backwork it and see the difference. That difference would be their margin. Better yet, just read their fine print - somewhere it'll say what % they add on top of on-chain txns.

Also; factor in traditional fees to transfer the money. If traditional fees are ~$75 and you're paying $44 then there's a deal there, but IDK your cirumstance. 

 I looked at the tx data in Sparrow. The fee paid to the miner was 6k sats (~13 sats/vB). So if i elected to pay 50k sats for their fee they are making a nice margin. 

@CashApp fees are more in alignment with tx fees you would expect when looking at the mempool. 

 I will need to try the free option and see how long it actually takes