All the factory Glock parts function just fine and are totally reliable. The tungsten guide rod assembly is WAY heavier than the factory polymer one, which allows quicker follow up shots. Tungsten should be more resilient than polymer, but I'm not sure if that is even an issue.

There are several drop in trigger connectors for glocks. Most of them just change the feel of the trigger. Lone Wolf is a popular brand. If you decide to change any of the springs DO NOT get a firing pin spring lighter than 6 pounds unless you want to run the risk of light primer strikes.