What do I need to keep in mind?

Make sure that the device can't fall into the water/the bath and isn't accessible for persons in the bathtub.
Don't leave the device unsupervised, when it is turned on.
Look for any damage on the device before every use. Don't use a damaged device.
Try not to use it for more than 30mins so that it doesnt overheat.
Don't let anything pierce the Soft-Mat.
Don't use the device with blocked openings.
Don't stand on it.
Don't use it when you're tired, don't sleep while it is turned on.
Leave the device and mat to cool down and dry before storing it.