The K6 Beer Equipment kit includes all the conveniences you get with the K3 kit, like an automatic pump-style siphon, an adhesive thermometer for the primary fermenter, and a full 27-page beginner's guide. But the K6 has a 7.8 gallon bucket and a 6 gallon glass carboy or PET (contrast two, 6.5 gallon buckets in the K3). The 6 gallon  carboy is good for secondary fermentations, but is big enough to house primary fermentation of a standard 5 gallon batch. The 7.8 gallon bucket is perfect for bottling, and is also a great choice for primary fermentation. Moreover, with these larger-capacity containers, it's possible to brew up to 6 gallons in a single batch.