Decking Board Question

[Brian in sunny FL]

I have a local guy selling 5/4 x 6" x 16' western red cedar decking boards for $16 each which seems like a pretty good deal.  I have some that need replacing and was going to use synthetic but may just use these based on the price and planned on building some large planters so can plane them down and use same material.  Two questions.

They are rounding on one corner, is that the top side or bottom side to hide fasteners.

Can you use hidden fasteners on any board or do they need to be made for it?  Which ones are popular?

[Snipe Hunter]

You really want to face nail or screw wood decking to keep it from cupping.
That is cheap. rounded corners up, Hopefully the mill ran the boards through the shaper/router rounding corners with the crown up.

Ideally 3 fasteners at each joist.

[greenacres2]

I did 2 small decks (12' x 10') 6 or 7 years ago, one pressure treated, the other Ipe. Used Kreg's blind screw jig. Neither deck has any sign of cupping. Did a bigger one (32' x 16') pressure treated mid 2023, used Camo''s blind screws--again no sign of cupping yet. The Camo system was faster & easier than the Kreg system. All 3 replaced 26+ year old decks that i used the 3 screws in the face--and that method worked long-term as well.

I really prefer the blind screwing for shoveling snow--too many times each winter!!

earl