Depends on what you want to do. I've made yogurt using the yogormet packets, and it tastes fine. If you only make yogurt sporadically, then this is fine. You don't need to run out and buy fresh yogurt just before making a batch.
However, if you want to keep making yogurt, using your first batch as the starter for the second batch, then the yogormet doesn't work. For whatever reason, the initial batch is fine, but then my secondary batch is watery. The third batch is a disaster. That doesn't happen though when I use store bought yogurt.
The fact that it doesn't make good second batches does concern me. Why is it different? I don't know. Anyway, what I've posted is the extent of my knowledge, and good luck.
Making yogurt is so easy!
Aven