I've had experience with phentermine in the form of Adipex-P in the U.S. and although it has psychostimulant effects, it's effects on the PNS is much, much more powerful. It increases the heart rate, skyrockets the blood pressure, causes anxiety, and it's just not a fun drug. Yes, it has "similar" effects to amphetamines, but it's psychological/behavioral effects are minimal compared to it's effects on the PNS.
It might work as a study aid, but with the kind of effects it has on the PNS I'd say it's not worth it.