Amphetamine should use the default 'launch at login' system
Currently Amphetamine launches itself at login via some unseen way. However, the default way (that all programs should use, and almost all do, since it makes clear what is and isn't launched at startup) is to add itself to the 'Login Items' tab in the 'Users & Groups' section of System Preferences. Its not a huge thing, but its nice to conform to platform standards :)
Amphetamine uses the standard approach (via Service Management framework) set forth by Apple.
This is documented by Apple here:
Amphetamine implements this using a open source project, LaunchAtLoginHelper:
If you’d like to request that login apps/items created using the Service Management framework to appear in System Preferences, please file a request with Apple:
To make an even stronger argument: Magnet.me and F.lux also deal with things concerning the screen (Magnet by being a Window Manager, F.lux by tinting the display) and they also have an helper app that lives in the menu bar. Even the direct precursor/inspiration of your app (Caffeine) adds itself to Login Items.
Having read the documentation, I still think you could code some kind of workaround and add it to Login Items. Every single user facing app that starts at login adds itself to that list. Here are just the ones I'm using: Alfred, Viscosity, Dropbox, 1Password, Magnet.me (app store app, so sandboxed!) and F.lux. In practice, (except for daemons, which regular users don't even know exist) users expect everything that starts at login to be at Login Items. Sort of the 'it just works' philosphy.
If you used Windows when you were young, you know what absolute hell it was to have some apps just magically start themselves with a custom solution, you not wanting those apps to start themselves, and not being able to find them in the default startup manager location..
Obviously this isn't nearly as bad but it would still be nice : )