What it is
Lightweight construction is the whole idea. An aluminium frame, composite panels and a small battery keep the trailer under many cars' braking limits, which removes the need for trailer brakes and makes the combination far easier to tow.
Why people choose it
Tiny does not mean cheap to fit out. Insulation, a heating source and a toilet still cost money, so a well-equipped 900 kg unit can cost as much as a bare 1,600 kg one.
What to check before you buy
Be careful about actual weight. Manufacturers publish an unladen weight; a battery, a full water tank and a heavy roof box will push you over the limit quickly. Weigh the trailer as you will actually travel.