We are celebrating our 25th year of installing almost entirely residential systems in rainy NW WA state, and I am not a fan of flashed L-feet! We used them for years, and after a few leaks, we moved away from that method. We have not had any problems with the Quickbolt attachments we switched to.
The problem with flashed L-feet is that you have to use a shingle ripper to remove two rows of nails that get in the way of sliding the flashing up and into place, and while it is possible to squirt some sealant into the lower row of nail holes, the nail holes at the upper row are too far under the shingle to access with a caulk gun, and so there will remain unfilled holes in the roof. One might think that they are too far up under the shingle for water to reach (that's what we thought!), but it isn't true. The roofs were we had problems were generally 3-5/12 roofs with lots of wind exposure, and the wind had no trouble at all blowing copious quantities of rain up under the shingles and leaking into the attic.
Our standard procedure now is to, 1) locate the rafter/truss, 2) drill a couple 1/8" pilot holes to confirm where the center of the rafter is, 3) drill a 3/16" hole for the 5/16" lag screw in the center of the rafter, 3) fill the probe holes with sealant and a roofing nail, 4) squirt sealant in the pilot hole, on the bottom side of the Quickbolt disc, and the lag screw threads, 4) send it home confirming that you have squeeze-out around the entire perimeter of the Quickbolt disc. Note that the probe holes that were filled with roofing nails are completely covered by the 3" diameter Quickmount disc, so there is no possibility of a leak. They have a 4" disc too in case your sins need a little extra attention. This method is much more reliable than flashed L-feet, and I am glad to see the industry is moving in that direction.
