I returned the treadmill a few days back; nothing worked..the belt kept slipping and the monitor didn't work..they didn't have any of those for replacement, so I chose a proform exercise bike.

I just did a workout for 20 minutes (I'll up it to 30 eventually, haven't worked out in a while) and I notice Im sweating alot..but, but I notice people always talking about how their "calves or legs look better", is it a good cardio overall, however?

Yes, it's a good cardio exercise. But if you want to TONE your upper body, you're going to need to do upperbody exercises.