I love my Solo but I cant suggest one over the Nano if the potential buyer is looking to maximize efficiency.
That being said the Solo is an awesome piece of hardware and it still sips herb compared to smoking it.
Should also mention the Nano doesn't need you to grind your herb.
Don't have experience with the eNano, but from pics and vids, seems like an awesome unit. I will be looking into them further, as maximum efficiency is a much desired aspect!
My Story and why having a battery sometimes is a blessing:
I just obtained a Solo 3 days ago, at the advice of an awesome FC member! I know now that had I purchased the Solo as my first vape, I'd probably never have purchased the EQ... The solo is a very flexible portable. Now, why would I recommend it over a plug in as the sole unit in your location.... well, as I stated, I received the Solo 3 days ago. Two days ago, major power outage in my area.... Thanks to having the Solo charged and 900 or so pages of advice (the Solo Thread) having been read, the power outage didn't stop me from medicating....
Thinking on that night, how awesome it was! Breaking in the Solo, 1/2 by candle light indoors and 1/2 under the stars......