The GeoSat one above is great. One of my favorites.
I recommend it (and some others) quite often.
The error comes in with the user.
No matter how good ya are, you need to just close your eyes and "use the force" for that last little bit. -
... and some dishes are off a little in their elevation...
... and the local magnetic error changes a wee bit every year...
... plus, compasses are difficult to read.
For tuning up BUDs, an inclinometer is useful, and some use digital levels.
The latter is great, but not mandatory.
Tuning a dish is like tuning a piano, there are many approaches, but the proof is in the pudding so to speak. Simple tools and carefullness is superior to expensive tools and rushing.