A few milliwatts can easily block the sensitive input of a Police Repeater on the other side of town.
FWIW, your "Hundreds of Milliwatts" are routinely used by hams to communicate world wide.
And no, a simple bandpass filter WILL NOT clean up this rubbish. Its output spectrum is the base-band signal repeated over and over, all the way up to VHF. It would take a very capable filter to pick out the single product required. This is NOT the way to design a clean transmitter.
It will not only cause interference, but it will interfere with EVERYTHING within range.
Most output filtering is a simple Low-Pass Filter which is designed to remove harmonics. But by definition, harmonics are an octave removed from the fundamental. This horrid device puts out a closely packed comb of spurii from DC to daylight. A simple passive filter will not even come close to cleaning it up.
You first start with a sound design, then add filters to clean up the last of any unwanted emissions. Not the other way around.
And because these faults have been well documented, this equipment would most definitely be classed as an "intentional jamming device".