We don't have a roof terrace but had composite decking installed in our garden approx 18 months ago.
We went for Millboard decking (never heard of it until Mumsnet).
I sent for samples first and quite frankly, after seeing a few composite deck samples from other places there was just no contest.
It was done by a landscape gardener who had never used it before but he was impressed with it and did a fabulous job.
He did a boxed in method ie built the subframe first then laid the deck planks on top.
Millboard sell special screws so the boards are screwed in from the top but they disappear into the top layer of the deck so they can't be seen.
Gardener and I were sceptical about the claims regarding "invisible screws", but they genuinely are invisible.
They also sell the black feet things you describe OP, and composite subframe products too, though we did not use these.
I think, if I remember correctly, that they do recommend them for roof terraces as they say they are not as heavy as timber.
It was not cheap!....but, it does look lovely and has made such a difference to how we use the garden plus, it makes it a lot cleaner underfoot when coming in to the house.
If I could just stop the birds from sh*ing on it, my life would be complete!