Thinking of buying the Whyte t129s, but not sure what flat pedals would be most suited for the xc / trail riding I'll be using it for. I looked at Nukeproof Neutrons and DMR V8s - prefer the look of the Saints, but worried they might be more DH/FR-focused and heavy on the climbs.
In the shortest way of answering this, yes, they will be suitable for trail/xc use.
All flat pedals are relatively the same. They only differ in the amount of pins, contact area, weight and their thickness.
You'll want something on the thin side for trail use, as you'll be pedaling quite a bit more than if you were on a downhill bike. This will help to reduce the amount of pedal strikes.
The weight is probably the biggest difference between all of the flat pedals. It is totally up to you as to what you find acceptable. For everyday trail use, the Saints should be fine and they should last quite a long while.
I think he is worried about the bearings being stickier than a trail specific pedal would be.
if he wants buttery smoothe pedals, downhill pedals are the wrong thing.
If you can handle losing a little energy/power to the bearings of a pedal, then the downhill pedals will be ok.