Very handy if you want to experiment with beer recipes during fermentation like different yeast, additives, etc. Brew up 5 gallons and divide into two carboys to do two different variations. Or use it to brew up an experimental batch that you aren't 100% sure, so you won't waste ingredients. Not so easy as a secondary to experiment with dry hopping since it's a carboy and not a bucket but still useful for aging a portion of wort if you want to try that too.

I like these for my smaller 1-3 gallon batches I do BIAB style on the stove top. Allows me to test out or fine tune a recipe.

These are great for splitting up 5 gallon batches to test different yeasts. I do this all the time when brewing ales. Awesome!

This is a great Carboy for those that don't like to make 5 gallons every time. I prefer a quantity of variety rather than a quantity of the same beer so this allows me to brew twice as much in perfect sized batches. This carboy is heavy duty and won't break easily. It also is easy to handle and move around even when full. I highly recommend this carboy to anybody who wants a medium sized carboy.

Great for small 3 gallon batches. I usually do a few 3gallon wine batches a year and this makes a great carboy for aging in. Some times I also brew extra wort and throw a gallon or two in this to try a different yeast.

I often split off lambic or stout beers after primary fermentation into separate vessels for extended aging. I like having something this sized exactly for half batches to keep air out. I have 1 of these small fermenter that has about 10 pounds of blueberries and 2 and a quarter gallons of lambic racked on top.

The only caveat is that they are very expensive, not much cheaper than 5 gallon glass carboys, so it seems like a better value to get the 5 gallon and just make more beer. However, if space is limited this really a great fermenter