Since you only have to do transactions to put a balance on coinbase and then can spend it over multiple transactions, does that help scalability?
I firmly believe in keeping your own private keys but I think it's an acceptable cost to give up ownership of a small fraction of your bitcoins and trust coinbase so you can do a few everyday transactions.
I don't know where exactly to draw the line but it would be 0.5-10%. Obviously a lot less if you have a large amount of bitcoin.
Are those services good for the ecosystem in total? How does it all work? Who gets the processing fees from the merchants running the Point of Sale?
In my country using bitcoin in every day transactions is quite difficult to do since we were not supported by bitcoin debit card or even coinbase. But for me I think it's really useful having a bitcoin debit card especially if the market will really adopt cryptos as a mode of payment, there's no need to cash out or convert into fiat. I just hope sooner my country will also allow this kind of mode of payment.