I can answer this, but I have no idea what I'm talking about so take it with a grain of salt.
Taking first up to redline and then not shifting out of it seems as if it would put a lot of unneeded strain on a few things. It seems like the tranny would strain out and cause damage to the synchros. I would also think that if you did this on a regular basis it would shorten the lifespan of the engine.
Hopefully someone that's actually knowledgable will chime in and tell you why I'm wrong, lol.
yeah i think the rev hang makes it worse, cause the needle stays up there for a few seconds. it only happend once, and i don't plan on doing it again. it looked like i had some room, then i saw traffic slowing so instead of shifting to 2nd i thought i'd just engine break till i caught up with traffic and would eventually stop.
i wouldnt do it in 1st gear, but any other gear that is acceptable
i bet you notice when you step on the gas in 1st and then let go it isnt smooth and your car just jerks.. thats why 2nd is the place to be if you're moving even a little bit... so no i wouldnt redline 1st then just let off the gas all of the time
when you let the revs fall with the tranny or let the car slow the motor, you are putting alot of stress on the rods. old muscle car guys always had this issue, they wouldnt dump the clutch fast enough and the rods would stretch.