What's the difference between Zinsser BIN and Zinsser 123?

What's the difference between Zinsser BIN and Zinsser 123? Zinsser B-I-N and Zinsser Bulls Eye 1-2-3 are both primers but differ in base chemistry and performance. Zinsser B-I-N is shellac-based primer, made with white pigmented shellac and alcohol solvent, considered strongest stain and odor blocker, excellent for severe smoke, fire, pet urine, nicotine, water stains, and for blocking tannin and knots, dries very fast in 45 minutes, can be used on many surfaces, but has strong alcohol odor during application, more expensive, and requires denatured alcohol or ammonia for cleanup, and is best for interior spot priming and severe cases. Zinsser Bulls Eye 1-2-3 is water-based all-purpose primer, low odor, easy soap and water cleanup, good adhesion on many surfaces including glossy, good for light to medium stains, drywall, wood, masonry, and general priming, can be used interior and exterior, more user-friendly for DIY, less effective than B-I-N for heavy odor and smoke. So B-I-N is heavy-duty shellac for worst stains and odors, 1-2-3 is versatile water-based for everyday priming.