I am not anti-Glyptol, but not pro-Glyptol either. I think if you are concerned with drainback, you could "port and polish" all the return surfaces and not have anything on there that could loosen up over the years
Drainback is only critical in mechanical design, meaning the those obstructions need to be fixed (casting flash etc). Glyptol doesnt help that.
The second benefit of grinding and cleaning everything up is to reduce the stress risers where a crack could start, Glyptol doesnt do that either
So basically, to me its a bit gimmicky, it does look pretty and probably wouldnt hurt, but I dont see it as a requirement
For me, the biggest issue with FE drainback is too much silicone on the end gaskets pushing into the drainback at the head. Once it gets in there it stops everything from the head......and Glyptol doesnt do anything to help there either
I dont think it'll hurt anything, but I still subscribe to "why bother"