I don't know what their outputs are. I just know they do both food and water, but do they put out as much food and water as a garden and purifying plant together?

Also oddly enough the Nuka Cola bottler also requires high Endurance as opposed to agility/perception

http://fallout.wikia.com/wiki/Fallout_Shelter_rooms

Essentiually it's those two rooms combined so you can use them to replace both types if you want to get more dwellers for other jobs.

They are helpful in the mid game if you want the majority of your people working in the ability enhancement rooms since the Nuka Cola plant produces both food and water with just 6 people (rather than 12 for separate rooms) ... if you are space constrained they can help since one room produces two resources ... for the end game it is less critical ... mainly the usefulness depends on your playing style and preferences