PepsiCo’s SodaStream has new competition from kitchen appliance maker Ninja. The Ninja Thirsti Drink System launched in late July. The company sent me a unit to try. Here are my observations:

— The primary difference in Thirsti versus SodaStream is that drinks are produced by the glass instead of by the bottle. With SodaStream and most other sparkling water appliances, including Aarke and Drinkmate, water is carbonated inside a multi-serve bottle. The user removes the bottle and pours in flavor syrup, shaking the mixture by hand. With Thirsti, water is drawn from a reservoir that is refillable and removable for fridge chilling. Changeable concentrate pods automatically release...