When you get one, take a look at the iTaste VV v3. It's a great little device that is around the size of an ego for around $25. It does a lot for the price. It'll check the resistance of the coil, display remaining battery life, and does both variable voltage and variable wattage. My husband finds variable wattage easier to vape with. It's like variable voltage, only once you set it you never have to set it again. With variable voltage, you need to adjust up or down if you change to a coil with a different resistance. In variable wattage, the device adjusts the volts itself to get you the same hit no matter what you put on top of it.
Another to consider, if you don't mind the larger size, is the MVP 2 for around $40.
Another to consider, if you don't mind the larger size, is the MVP 2 for around $40.