so normally in PF when trying to interact with tech-based subjects or items you are counted as untrained, so picking up a mono sword to use you are not trained in it even if have skill in swords. The feat allows you to be counted as trained when interacting with tech (as default PF characters really cant)
Since everyone is counting as having feat the first statement is moot.
No, so no one is taking the favored classes, d20 got a boost in skills by making a knowledge 1 skill saving lots for those that take each skill one on one, and PF and SF have gotten a boost to skills points AND merged skills so don't need to take separate skill for things like stealth and perception. By allowing specialized skills they can get 2 more points up on skills they want to be good at.
Yes, that will be like going to a merchant. There will be some items you can sell for more, anything analog can be easily checked by the merchant and could get you the std 50% but any tech, they go no idea if this will break 5 min after you leave. Again some merchants may be able to check better than others so there are chances you get more, just the std is 10% ( I was a bit surprised till I thought about it. A sword you can see check easier even magic can be identified but tech there always can be an unseen problem with it.)