Obviously, my advice is to not walk on the roof. It creates mechanical damage from foot traffic and the warmer it is, the worse you can damage it. It's not like it's going to cause a leak immediately but it certainly might give the adjuster a reason to bail out if you ever need to make a claim.
Get cougar paws for walking on the roof or some Vans skate board shoes with gum soles.
But I agree with the above, if it's more than a 6/12 just stick to lights on the eaves.
If you insist, then the setups in the links above look similar to what we use. I'd definitely use the included anchor. Install on your ridge under a shingle and use multiple holes with screws.
For testing purposes, I have suspended my 180b self from a single deck screw of 1.25" into a stud. For a roof harness, I would use no less than 6 2.5"-3" screws because I'm a chicken and really don't like heights and falls and I crawl on roofs all the time.
Full disclosure, on my home, I don't put lights places I cannot reach with a single story ladder.
Infinity Roofing - https://linqapp.com/jason_duke --- JasonDuke@InfinityRoofer.com --- https://infinityrooferjason.blogspot.com/
