Convenient, certainly. Efficiency has several factors. It does seem efficient, but part of efficiency is cost, which is buried in the price of the product or service you're paying for. The fees associated with different payment schemes vary, and I believe the trend is for the seller to have more choices and so market pressure to reduce transaction fees, but right now, it's costing a whole lot of money that we simply have no way to see.
But I'm a fan of no cash while traveling. I just got back from a 4 country trip and didn't hit the ATM even once.
Public transit was once the bane of my cash avoidance plan, but everywhere I went, they had a mobile app. You just download it, put your CC# in, and buy a ticket. Often they'd also take CC when you get on the bus, but that takes time and the driver's attention. With the app, you just get on through the back door and show the ticket on your phone if asked. I saw some people scan the ticket QR code, but not many, so I figured it was optional.