If you are not using the Short Circuit like a cheap-ass, then you should have no issues with this wrench in its current state.
The metal regeneration being halved is actually a good thing with this wrench, as the teleportation to spawn is actually very powerful, especially on larger maps. You build on the other end of the map, you teleport and instantly piss off the hale that now has to run all the way back to the main spawn.
It makes Engineer a little bit harder, sure... it also makes them require skill instead of just needing the Short Circuit to win, as they cannot build their sentries directly to level 3 with a teleport entrance and exit being built at the same time.
Giving full metal back when you are still able to regenerate 10 metal per 'tick' feels unnecessary to me. By the time you have successfully teleported, I would expect the Engineer to have recovered at least 60 metal, which combined with his current metal, I expect the player would be able to build a new machine within the next few seconds.
