I recently put inserts into a Strat neck I've had since 2002. It had been on and off a lot, and two of the holes got stripped. I repaired it with toothpicks and glue originally; however, this is only a temporary repair. You have to re-do it almost every time the neck comes off. So I decided to go with inserts.
I got a kit from eBay and did the whole thing myself by hand and eye with a regular power drill. The kit specified drill bit size in the instructions, and came with a short, allen-headed bolt to put in each insert to wind them into the neck. After I put each one in, I re-fitted the neck to make sure I hadn't screwed anything up. Quite surprisingly, everything went just fine.
It's true that you feel comfortable tightening the screws more, and I'm not afraid I'm going to strip the wood. I have no idea if it produces more sustain - the guitar was already fine in that regard and I haven't measured it. It's definitely going to help with removing and re-attaching the neck, of course.
In all, I would definitely do it again, but only if I had the same problem again. I'm fine with metal screws going into wood; that's a very very strong join.