BTW if you are looking for a small cheap discrete set up the Smok 4 running on the small size ego pen batteries is brilliant - totally concealable in your hand and great as a back up.
For emergencies I always have mine in an old tobacco pouch when I am abroad or travelling, with a wee bit of Kanthal wire, a cotton wool ball and have mini nail clippers on my key ring ( I was a pipe smoker and always had the trade mark black fingernails from tamping down the tobacco so I carried one of these for years.)
You don't need tools to tighten down the coil screws and as I absolutely know - if the coil dies 9 wraps of 28 gauge round a cocktail stick/toothpick, available in any Spanish bar gets you going again and comes in around 1 - 1.2 ohms which suits this tiny thing just grand.
While they are not the greatest those small pen batteries are available partially charged at any Spanish tobacconists vape shop or supermarket.