Fewer corners, less to catch
The inside of a half-round has no square internal corner for grit and shingle granules to pack into, so it tends to self-clean better than K-style in the same conditions.
It carries somewhat less water than K-style at the same width, so we usually compensate with a larger size or an extra downspout.
Copper
If you are considering copper, half-round is where it looks best. It arrives bright, weathers to brown within a year or so, and eventually reaches the green patina people picture. It is a significant premium and it is a genuinely permanent gutter.
What’s covered
Ten years on our labor, and a 50-year limited — lifetime for the original homeowner — warranty on the shingle itself, backed by Owens Corning.
Full limited-warranty documentation is provided with every contract and governs in all cases.