a welded seatbar is $100 and crossbar is $65, and the passenger seat plate is $60.
if you can return the seat plate and crossbar and get the welded seatbar it will perform better than the seat plate. You don't want to be in a rapids if this thing slips. maybe you won't have any problems since you are using a lowback seat.
For your passenger seat this mount is fine as they are not generating as much force against it like in a hard row its nice to remove the seat when there is no passenger.
If you want I can find out who Andy/Bax uses. The've got a custom seatbar with plate welded on it as well as a footbar drop welded below it. So it replaces the $175 of components for a seatbar and footbar and is also lighter than the combo. I'm guessing the pricing is similar but it would shave a few pounds off your setup and be less complicated.