the use of fasteners are really the issue with me.
There are many fasteners around now. The long pole nail and the ferrel are things that are of days gone by and really do not work for very long.
What I really like are the contraptions that hook into the gutter front and back and then screw into the facia at an angle downward and do a much better job.
Actually any fastener that screws into the facia is one of better quality.
Then too, the "fall" or slope of the gutters to the nearest down spout is another thing that many un professional people seem to leave out. Before the gutter labor bill is paid, get a level and check for a fall on every straight peice of guttering. If the gutter is level, it will not drain properly.
Then, I do not like a space between the gutter trough and the actual facia. I like the upper overhang of the shingles to actually over hang into the trough. Some of the roof shingles and the gap of the gutter and the facia cause the water to drip into that gap and not into the gutter trough.
You never know the problems until the next heavy rain.