The answer is yes and no. If someone challenges you to a fist fight, is that a good or bad thing? The answer would depend greatly on how you view violence and the reason(s) the other person wants to fight you. If you chose to fight, would you be ready?
You don't have to scour the internet to find fitness challenges. Challenges are everywhere.
Here are 3 things you should consider if you do start a challenge.
Is it good for me?
Painful movement can and does happen. Are you using exercise to "get in shape?" The best results from exercise are when the person is already "in shape." If pain is the end result of exercise, either the exercise is too difficult or you are doing it wrong. Stiffness and soreness are not the same as pain. Pain, by definition, is when you are avoiding normal motion - aka compensating to complete the motion.
Can it be sustained?
If programs like K900000-Z were the right answer for the masses, then we would all be doing it. Sometimes small challenges are great at getting you from point A to B. There is definitely a time and place for intense or slow paced exercise programming. If you had to stop your program because of injury, then it is not sustainable. We do not all fit in the same box, and cookie-cutter approaches tend to injure too many people.
What happens when it's over?
If you get to the end injury and pain free, what do you do? On to the next challenge? Have you ever had the meh feeling at the end of a long journey? Movement has been replaced by exercise and fitness. If you believe that exercise is what makes you fit, then buckle up - you are very likely to discover injuries that you have never had before. People don't become fit just by accident. Yes genetics helps, but the most fit people in the world don't necessarily go to the gym, or even do "challenges."
Fitness is continuous nutritious healthy movement.