This little device if fabulous - dispensing 1/2 a shot of your favorite 'additive' (be it an adult beverage or something else) to the container.... I have both the 20 0z Tumblers AND the 30 Oz tumblers and I've bought Flaskaps for both of these containers.....
I would strongly ADVISE AGAINST putting these in the cup holders of your autos (especially if filled with 'adult beverages' because this would be considered an 'open cantainer' and could bring down some heavy fines on the operator of the motor vehicle.....
When riving I keep this in the trunk of the vehicle - it usually will NOT spill out it's quite good that way) and once at my destination (usually a golf course it gets attached to the container.....
It is a bit pricey but considering the machining and design that it takes to make this device it's well worth it !I
I've used it every time I'm Gofling and have even ought a few as gifts for my friends as well.