Questions are OK, you will have many.
I have the batt backup in my D100 and D180. Make sure you read the section on the removal of the "keep alive" wire.
Unless you are very familiar with glass panels, I suggest you read both manuals thru and thru before starting. This is a feature rich device and you will have questions.
There are several people who post here who have installed Dynon.
Yes, Stein does a good job.