im new to kendamas and i was wondering are there any health benefits to playing ? i heard its good cardio . can anyone confirm that ?
um, cardio I don’t know, unless you play for like, hours upon hours on end. It’s very relaxing and meditative so in that aspect I think it’s very good to your heath. Not so much when you drop it on your feet. XD
IMHO, kendamas help with strengthening the knees, builds up focus and improves overall balance (of your body), not to mention improvements on patience. Also very relaxing and meditative as mentioned earlier, it also helps to build up some sweat, since nearly every part of your body is involved (knees, calves, arms, hands, lower body).
My yoyoing friends (both Dimi and Zafran) also told me that it helped them improve some core aspects of yoyoing as well.
Cardio? Doubtful to say the least.
I find a good session tends to pop a few creaky stiff joints into place, which is always great. Keeping the knees lubricated probably isn’t going to hurt you as long as you don’t play 8-hour straight sessions every day at which time maybe you want to scale back or break it up a bit. 
I believe at least in the early stages of learning there’s a lot of hand-eye coordination going on that’s not found in the same way for yoyo. Yoyo is a reactive and predictable thing… before long, you land a trapeze (as a simple example) because when you swing around and apply just the right tension, the yoyo almost has no choice but to hit the string. It’s a muscle-memory and “feel” thing.
With kendama, at least as a beginner, I’m definitely AIMING for the hole when I do the spike that ends an around the world. Not quite the same for basic pull-up spike, but the sideways ones where you are looking at the hole and trying to stick it? Hand-eye coordination all the way.
http://kendama.co.uk/benefits.html
Looks like you get cardio from it
All those squats will get you the butt that drives the chicks crazy.