This is our 6" seamless gutter machine. We can make any length of gutter you could possibly need.
The advantage of seamless gutters over the typical 10' pieces of gutter are many. One there are less seams to caulk and leak from. Two it looks nicer. Three it is easier to slope and make the water flow in the direction you need.
You'll want to use 6" seamless gutters any time your roof pitch is a 6 or more. Otherwise the gutters will overflow.