Not wanting to hijack other threads about primers. I have done lots of painting, but it was mostly in the days of oil-based primers. I recall reading that the latex interior-exterior stain blocking primers are too ridgid/stiff and do not hold up well on wood as they do not stretch as the wood moves. Recommended for just the stains/knots. My limited experience seems to bear this out. But others are enthusiastic about the 1-2-3. I have used it for interior.
I have some exterior wood about 7 years old which has been painted twice and badly needs it again. I need a better primer.