Here are the pros of the 5BX/XBX style workout:
- Stretching improves flexibility. Flexibility improves your "fitness age" and helps prevent injury.
- The calisthenics are compound movements recruiting large groups of muscles together. This helps improve (initially) or maintain (ultimately) your muscular structure in a balanced and meaningful way.
- The aerobic activity helps burn fat and optimize the aerobic metabolic pathways.
The cons of this type of workout are:
- There is not improvement on your muscular structure beyond your own body weight. In short you will only get so strong with it.
- The aerobic activity kind of works against the calisthenics as far as optimizing the types of metabolic pathways that support strength training (anaerobic/calisthenics) vs endurance training (aerobic activity). Since you aren't really pushing your strength in this plan it's not that bad.
That said it all depends on what you want to get out of your exercise. The 5BX/XBX style of workout provides an overall fairly balanced approach to getting and remaining fit. It's not the type of workout that will help you excel in sports, but it will help you maintain a modest amount of fitness that will prevent injury and help you live a healthier life. If that's all you want out of your routine it's a good plan.
The important thing is that you have a plan you can follow and stick with for the long term. If it's not that type of plan, then you can start playing by substituting other exercises that perform the same type of work just for a bit of variation.