I seem to remember PNW used the same OEM posts as well. I’ve had several Brand Xs (family fleet, init) and they’ve all just worked. Good sealing, completely reliable.
The only reason I switched from Brand X to OneUp originally was the ability to squeeze a longer drop into less overall length – a critical concern if you’re a shortarse like me with short legs on a frame with a short seat tube.
However, I had reason to drop OneUp a line after my new post (the second one I’ve got from them) developed a score in the stanchion, and their after sales service was absolutely superb. I had a brand new post in under a week, with the suggestion that I hang on to the old one and use the non-scuffed bits for spares.
Unfortunately, they shipped me a V3 post, so if anyone needs a spare cartridge or lower tube for a V2 210mm dropper, I’ll be happy to send it your way in exchange for a donation to MND or a similar charity.
Summary: TransX/Brand X/PNW posts are fab, but if you need more drop for length and great support, I’d say OneUp is worth the extra cost.