The max. allowable input voltage with a X 1 probe is +/-100V regardless of the voltage measurement range setting: +/-10mV, +/-20mV, +/-50mV, ..........+/-10V, +/-20V, or +/-50V.
Like many other oscilloscopes in the market, the input of the probe and the input of the VT DSO are NOT galvanically isolated from the computer connected. For many computers (typically desktop PCs or laptop PCs with a built-in AC power supply adapter), the ground lead of the probe is connected to mains earth. This is not a problem if the circuit under test is floating (i.e. isolated from earth). Otherwise, you MUST make sure that the ground lead of the probe is connected to a point on the circuit that is also at earth potential.
For the ground loop issue and its possible impacts on the measurements and USB DSO, see video:
https://www.youtube.com/watch?v=0Vo2u11V3fU