Fitbit

I wear it on lymph arm with surgeons blessing. No problems. 

Best to check with with your specialist. 

I have been wearing one for 2 years now. They definitely help you to be more active. I have one that also monitors your heart rate, as the heartrate thingy sticks out below the band I would not ever wear it on my lymph node removed arm. Even though I wear it loose, there is often an indentation, particularly in hot weather. Works just as well on the other arm (you can change the settings if it is your dominant arm or not). 

I’ve bern told no. I’ve had to switch mine to the other arm. It’s taken alot to get use to

Just like a bangle should be ok. Just be sure it's not too tight and that your skin doesn't get irritated from it. I was thinking of getting one to help in my back work fitness plan ....

As long as it's not tight it shouldn't matter. 

I don’t. I wear mine on the other arm just to be safe.