I personally like the Crius II more than the Nano. IMO, bottom AF gives much better flavor. My son, only vaping since last November, started off with an Engine Nano and a Battlestar mod. He was very happy with it until a month or so ago when we were on a weekend trip and he left his vape gear at home. Of course, I travel, even for the weekend, with a fully stocked case of extras.
I let him use my Therion 75c and a Crius II and he was spoiled quickly. Took the Therion back but let him use a Crius II and he prefers it. He isn't as careful as I am and has had no trouble with the Crius leaking. With any bottom AF, there will be some light condensation on the top of the mod from the AF holes, but it is light and easily wiped off.
I do hope you enjoy it!