The best is the spikey platic one, the worst is the metal one that looks like a flap over the muzzle.
Hardly any method involved putting it in. Head in headgate, loosen the wingnut put ring in and tighten wingnut. For removing put head in headgate loosen wingnut and pull out. Sometimes the ring grows through the septum and you end up with both knobs in the same nostril. From experience its better to push both through the septum to the other nostril and remove one knob and then the other pulling it back through the septum again.
It helps if you can start the calves on feed before weaning if your pasture isn't great, put rings in and leave them with the cows for about a week, then you can remove the calves if you want, but keep the rings in for now incase some cow decide to come fetch the calf.
Success rate is about 95% for me, long teats and first calvers that refuse to wean the calf can sometimes cause problems, but overall a great invention. They last a long time, but you'll probably break a few each year when removing them.
Haven't used them myself, but 2 neighbors tried them this year and both like them. Only complaint was that you cannot leave them in too long or they can make sores in the noses. One said they did only 5 days but that was enough and loved them, and will use them every year now. For me, I like the idea of it, but the way we are layed out, we cannot go around to that many pastures and catch everything twice or 3 times to prewean and do nose weaners. I think those that have their cattle in one or two groups would work great.