The Schlage Everest has a side pin on the bottom of the plug that has to be pushed by the original key to allow it to operate the lock. Here's what I mean:
http://www.lockwiki.com/index.php/Schlage_EverestThere is a special tension tool made by peterson's that goes deep into the the keyway to align that pin.
I've never picked one of those, but I suppose it doesn't have to be picked "per se", just pressed so it aligns with the plug. That pin is the same on all those locks. That (in addition to picking of course) will let the plug rotate. There is a post about that tool here:
viewtopic.php?f=3&t=6047Matt Blaze has another method of tensioning the lock that consists in cutting a key in a way it goes to the end of the keyway and still gives you space to insert picks. Here's the link:
http://www.crypto.com/photos/misc/everest/Basically, to answer your question:
1. yes, there are such tension tools
2. Yes it's still able to pick a lock with it
3. Personally, I think it would only be better on very specific locks like the Everest, for the reasons Gordon described.
Hope I helped

Go ahead, keep plugging away, picking on me! You will end up on bypass or with rigor mortise.
- GWiens2001