I seem to see three types of backflow preventers:

1. valve + vacuum breaker
2. double-check-valves
3. double-check-valves + pressure regulator

If I don't need or want pressure regulation how do you compare 1 vs 2 above?

This would be for lawn irrigation or water-powered sump pump.

Examples:

https://www.homedepot.com/p/Zurn-3-4...720A/100197627

https://www.homedepot.com/p/Febco-3-...-850/205888731

https://www.homedepot.com/p/Apollo-3...4A2F/307723094