Is it safe to use hand held back massagers during pregnancy on your stomach?

Okay well my friend has a handheld back massager, it has a REALLY low setting like that just feels like reaaalllyyy light and good on my stomach, then it hit me, oh no! What if it's not good for the baby! I am 21 weeks along (it's a girl :D). I just wanted to make sure it's okay if I don't apply any pressure, and keep it on it's lowest setting without heat. It basically feels like someone is rubbing my tummy, but everyone's hands get tired because I never want them to stop! Haha please write back asap :) Thankyou<33