An internally geared hub is less efficient in general, but a (more expensive) mid drive makes it a non-issue. It's designed for ease of use, and less maintenance than a rear derailleur. Being a CVT with the NuVinci hub making it less efficient than geared IGH's is something I've never heard of. It's considered a premium IGH, like a Rohloff. I don't think it has the same gear range, but it's a great IGH nonetheless. I had it on my Xootr Swift. My only gripe was the weight, because it made my folding bike a boat anchor. An electric bike negates that issue.

As to efficiency in general, mid drives are definitely more efficient. Up until recently they were also hella' expensive. The pricing for them has now become reasonable. An IGH isn't always necessary either. I'd opt for a non-IGH mid drive and enjoy if that's your preference.

Me, I'm still waiting for my Lectric XP Lite JW Edition to ship. Rear hub, single speed, BMX style, 14+ AH battery... All the fixins for a simple, enjoyable ride.