Hi FullyCool
For an exposed hairline there is a clear choice - Walkers 3-mil thin lace support tape. In my view it is the only tape that is thin and discreet enough for an exposed hairline.
For an unexposed hairline you could use any tape, but can you really say your hairline is always going to be unexposed? What happens when you are lying back in bed or on a sunlounger, or walking into a strong wind? Unless you are OK with the tape being visible and possibly giving away the existence of the system, you have to assume the hairline will sometimes be exposed.
I would recommend detaching the system and reapplying fresh tape every 7 - 14 days. I would say the average is about 10 - 12 days.