Is there a risk with Fitbit watches? Should I avoid using smart watches of any kind?

I do not recommend Bluetooth-enabled devices, considering how much they emit, and how close they are to the body.

Considering that phones are completely unsafe (and should be re-classified as a Class 1 carcinogen according to many scientists), it's logical to assume that Bluetooth devices carry the same risks.

I recommend using Bluetooth devices very sparingly, for short periods of time, or opting for the very few "wearables" that can be operated while on Airplane mode. The Oura ring is one I recommend, and I keep mine on Airplane mode all day, unless I'm transferring the ring's data to my phone. https://ouraring.com

This video on my YouTube channel goes into more detail: