I fly with 2 Grands all the time. One in my carry on with my RBA supplies, including scissors for wicks, and one on my person that I either put in a little pouch on my bag or in the little personal items tray. I have been asked what it is a couple of times at smaller airports, but once they look at it outside of the x-ray machine, they immediately know what it is. Batteries go in a little nylon pouch in my carry on. Never any problems going through TSA. The only thing I get from time to time is, "Oh, I have never seen one like this before." I have been secondaried more times than I can remember for packing my bag too densely and having too many electronics / cords, etc. but never for going through with a Reo.
Like all vaping equipment, if it is topped off with juice, you might get some auto-squonking and leakage due to pressure / altitude, but even that is pretty rare. I try to remember a little square of paper towel in the event of any issues of that nature. Whichever Reo I am using at the time rides in my pocket on the flight.
Make sure your liquids are in your clear bag in the carry on or in your checked bag, if you do that.