Amazon recently introduced Bid+ within their PPC system. Again, Amazon taking features straight from the Google AdWords playbook.
Will I be using this feature? Heck no.
These kind of features, especially in the beginning, never fare well for the advertiser. Essentially Amazon will jack up your bids in scenarios in which it sees fit. In other words, you totally lose control of how much you are bidding.
Amazon would like you to think that this will increase conversions but in reality it will just increase your ad spend.
In summary? Save Bid+ for a later date when Amazon has a more robust feature set. It might be good in combination with features that don't exist yet.