What the machine on the trailer is actually for
A seamless gutter is not a different product from a sectional one. It is the same aluminium coil, in the same profile, formed at the kerb instead of in a factory. The entire benefit is that the piece can be made exactly as long as the wall it is going on, and understanding that makes it obvious where the benefit stops.
Seamless removes the joints that leak least, and leaves the ones that leak most
Sectional gutter comes in lengths of about ten feet and is joined with a connector every ten feet along a run. A 46-foot elevation therefore has four joints in it, each of which is a place for sealant to fail, for debris to catch on the lip, and for the two pieces to move against each other as the metal expands and contracts. Removing those is a genuine improvement and it is why seamless has become the default on almost every house in this metro.
But now count what is left. On a straight run of a plain rectangular house, seamless means one continuous piece per elevation and the only remaining joints are the end caps and the mitres at each corner. That is the honest description, and it matters because the corners are where gutters actually fail. A mitre sits at the point where two roof planes meet, which is where water from both of them arrives at once, at speed, in the greatest volume anywhere in the system. If any joint in a gutter is going to be tested, it is that one.
So "seamless" is doing something slightly different from what it sounds like. It removes the joints in the calm part of the run and leaves the joints in the violent part. That is still worth having, four fewer failure points per elevation is four fewer, but it explains something people find puzzling, which is why their seamless gutter is leaking at the corner three years in. It was always going to be the corner. Nothing about seamless was ever going to change that.
Which is why the corner is where the actual craft is. A mitre can be hand-formed on site from two pieces cut to the true angle of your roof, or a pre-made factory strip mitre can be riveted between two runs. Factory mitres are fast and they assume 90 degrees, and very few houses are exactly 90 degrees once you account for the way the roof was framed and how it has settled. A mitre riveted into a corner that is actually 88 or 93 degrees is under load from the day it goes in.
We hand-mitre, and it is included rather than an upgrade line, because on a gutter the corner is not a detail. It is the whole ballgame.
One practical consequence worth knowing: because a seamless run is a single piece, a damaged section cannot be swapped for a ten-foot length. The run is replaced or the section is repaired in place. In practice that is rarely a real cost, because at $8 to $13 a foot even a 40-foot run is not an alarming number, but it is the trade-off nobody mentions.

Why it has to be made at the kerb
The machine is a set of rollers on a trailer. A coil of flat painted aluminium goes in one end and finished K-style or half-round profile comes out the other, at whatever length is asked for, cut on the spot. A 46-foot run means feeding it until 46 feet of gutter has come out.
That is why it is done outside your house rather than at a depot: a 46-foot piece of formed gutter is awkward to the point of impractical to transport, and it damages easily. Forming it three feet from where it is going up eliminates that entirely.
It also removes lead time. There is no waiting for material to be cut to size and delivered, which is why a full house can be measured one week and installed in a single day the next. And it means a run that turns out to be 46 feet 4 inches rather than the 46 feet on the measurement is simply formed at 46 feet 4 inches.
The coil itself is ordinary painted aluminium in standard gauges, and gauge is worth asking about. Thinner coil is cheaper and dents more readily, from ladders, from branches, from hail. It is one of the quiet places a low per-foot quote comes from, and it is not visible in a finished job.
When sectional is genuinely the better answer
Rarely, but not never, and it is worth saying rather than pretending seamless is universally correct.
A very short standalone run (a porch roof, a bay, a shed dormer) gains almost nothing from seamless, because a ten-foot sectional piece has no joints in it either. Where that is the entire job, sectional avoids bringing a machine and a trailer out for one length, and it is cheaper.
The other case is a run that has to be assembled in place because there is no way to get a formed 40-foot length up to it: a courtyard with no access, a run above a conservatory or over a neighbouring roof. It is uncommon and it does happen.
Both are exceptions. For almost every house in this metro, formed on site to the length of the elevation is the right answer, and it is what we quote unless there is a reason not to.
What the job covers in Charlotte
What we cover
Seamless aluminium gutter formed on site across Charlotte and the surrounding counties, in 5-inch and 6-inch K-style and half-round.
Target outcome
A run with no joint anywhere along its length, and corners hand-mitred to the actual angle of your roof.
Decision point
We are straight about what seamless removes and what it does not, so the upgrade is bought for the right reason.