I have a small goniometer myself. I can get by pretty well with that. But for the wider knives, it was too small. I could only measure knives near the tip. I didn't think that was accurate enough for the larger knives.
In my search, I came to one that was designed slightly differently. The knife is now behind the large protractor and not between the laser lamp and the protractor (see photo).
I ordered this one and now use it regularly. I like it very much. This goniometer is also made in Germany. Below is the abbreviated link to the product. The goniometer is sold through Ebay.de. If you enter 'goniometer' as search term there. Then you will get there automatically.
https://ap.lc/MbDjm