The NFT does get some bad press, I reckon you’ll be fine on a rigid, although that depends on age. When I got into mountain biking in the mid nineties I rode Walna Scar, Garburn Pass on a fully rigid and thought nothing of it. I’m pushing 40 now so I can just about get away with a Ti hardtail. I find the NFT is a great trail for getting fit/training, there are better options though – it is showing its age, but it does stand up well to adverse weather, except for the North Shore sections that is, watch them in the wet. I think they should have used Cedar wood which would have been pretty grippy, but they put something in which is lethal in the wet on some of the adverse cambers.
They took some North Shore out a year or so ago due to people having accidents. I’m glad to see that they are now replacing the lame chicken runs they put in with boulder sections, so the trail is getting some of its cajones back.
It’s not the best trail in the world, but it’s been around a while now and it’s still challenging to get round without dabbing (seriously, try it). Also if its quiet try getting round in under an hour, if you can then you’re doing OK 🙂 If there are people around though I’d just sit back, enjoy it and soak up the views.