To the two previous posters: read the requirements section BEFORE YOU TRY AN APP OUT. 10.5 is required, it is required for a lot of apps now, so deal with it.
For those with 10.5, the app works as advertised, albeit with a very limited set of conversions. Since it is in beta, I imagine more will get added eventually. The app is OS, so I think you can download the source and add in your own conversions, too (not that I've checked). If this app had Stress/Pressure conversions, I might use it more often.