1. It works on all reincs which have additional stats/rubies etc. used and after time out you have less than already spent. If those additional rubies/stats are not assigned then there is no reset.
2. You can't use those temporary stuff if you already have bonuses from them. Doesn't matter if they are from perma or temporary ones.
3. It works only once a month after expiration and it's cost should to be calculated. If you want to use them only for reset purpose there is 1 month delay and some of them are more expensive than respec item. Most of them can help to fix builds though. Especially if you need to do it on several reincs.