“Without a heart rate monitor” is not allowed. 🙂
1) We’ve moved away from the nose breathing idea because people new to training can still nose breathe above aerobic threshold. It works for athletes with a long training history and a big base. But it won’t work for those new to training or coming from a predominantly high-intensity background.
2) Yes, for sure. If you have sinus issues–infection, injury, etc–it won’t work for anyone.
Better than the nose limiter is a drift test.