The only issue is you can only change cash into BTC, not coins.
This is from their website :
https://www.coinstar.com/bitcoin"Only cash is accepted. Coins cannot be used for Bitcoin transactions."
So you'd have to change your coins into bills and then use those to buy BTC... which means more fees.
but what if the machine had a LN node? The user would have to download an app (ln wallet) to their phone obviously, but then the UX could just be:
- walks up to machine
- taps phone onto machine to create channel
- dump physical coins into "coinstar" machine
- machine counts money, sends tx to user
- user walks away with BTC in a LN wallet.
Then you could handle tx as low as a few dollars. Still taking the 10%, you could even just program that 10% right into the fees since these would also be private LN nodes (for security reasons).