My old boost gauge used to be accurate until I punched it then it read 10 on the vacuum when the car was off. I think I might buy some water filled autometers next time.
In a strict sense, the Autometers are not the end all when it comes to accuracy if the quoted accuracy values are representative of real-world performance. The specs I have been quoted are 2.5%, which is nothing to brag about. A good instrument will be 0.5-1.0%...but those are far more expensive.
For the money (and application) you are OK with Autometer. Besides, when you are trying to take readings at a glance in a moving car with a relatively thick needle, 2.5% should be fine.