It's an investment and it pays off over time. However, if you're serious about yoga and want to develop a lasting secondary education, it's worth it. Teaching yoga classes full time undoubtedly means that you'll get more teaching experience in a shorter period of time. I hope that, if it seems harsh to you, that means that you have a better teaching organization and that you are not being exploited like many teachers are.
If you want to gain followers, teach at a gym or fitness center; this will almost always cause people to attend other classes in the future. And a big question about safety, the truth is that I think a lot of the ways yoga is taught are dangerous, even with great alignment instructions and practical settings. Crowded classes may be less pleasant for doing yoga, but they are usually better for teachers, since medium and small classes are a guarantee that the teacher is getting peanuts. In the process, you'll end up being an entrepreneur, event planner, marketer, perhaps course creator and a fierce model who evades the routine of income or fatigue that usually affect yoga teachers who were once passionate.
I also want to say how important the experience of being a student at a great yoga school has been and continues to be for me. Therefore, places that charge per class at least have the POTENTIAL to pay teachers much more fairly, and it's very likely that those teachers were some of the few who made a lot of money. I think that's a more common salary structure now, especially if the studio is in a nice area or in a place where a lot of people do yoga. If you're not doing it for income, teach in places where it's free for people who come with legitimate needs.
If you don't develop a niche in your teaching and transfer the knowledge of the group class to workshops and other more specific and higher-income angles for your teaching, it means that your skill set and your means of income are still limited. I have been doing yoga for years and once I applied to enter what was being promoted as a very exclusive teacher training course with a competitive application process and limited places available. I considered it because I loved yoga, but in the end I couldn't imagine that it would be financially worth it, at a time when it would have been difficult to afford it. I was working full time and trying to teach as many classes as I could (initially I wanted to teach full time, but it was difficult to earn money).
I discovered that teaching 3 classes a week was too much for me, in addition to working FT and, although I was teaching 2 classes a week, it jeopardized leaving enough time for my own practice.