We've had a bonding gutter, for as long as I can remember, with no problems.
Up until about 2 years ago, next door had plain tiles, whereas we had profiled tiles. When nextdoor was re-roofed they went to profiled tiles also.
I never noticed until last week that their headlap is about 40mm, whereas ours is about 75mm.
(Incidentally, in reducing their headlap to below the minimum recommended, they would have saved the cost of about 30 tiles and 2 lengths of tile batten! I.e. one row of tiles per pitch.
)
I noticed last week, only because I was stripping our one side so that I could replace the felt with breathable membrane and install additional ridge vents. I maintained our headlap at about 75mm.
There was one ridge vent installed, but a) whoever installed it did not remove any felt, b) they did hack out some of the ridge beam, instead of reducing the length of the vent, and c) they left the little bit of additional membrane and brackets that comes with the vents up inside the vent reducing its efficiency even further!
So the reduced efficiency vent was venting the space between the tiles and the felt!
We also have now a gap in the middle of our ridge beam between two rafters.