I have only one of the new AW 17670's. It's a tight fit in a 2x123 Aleph body like the ones on my A19 XR-Es (peel off the label) but it does fit.
Around the house, I usually run my A19 XR-Es in Pineapples, which fit the 17670 easily.
A 17670 has more watt-hours of capacity than 2 RCR123's, especially at the high current draws of many of our flashlights.
It is also cheaper than 2 RCR123's.