My cheap Metabo mitre saw works fine, but I realized that the cuts that it made weren’t perfectly perpendicular. This was especially noticeable on mitre cuts. Luckily, despite the manual not mentioning it, it is possible to adjust the saw. There are two end stop screws, one on each side. The one on the right (shown below) adjusts the 0 degree position, the one on the left adjusts the 45 degree position. You have to release the black handle to be able to make the adjustments. I used a 3D printed square piece held against the table and the saw blade, but any sufficiently small square device should work.
