You must read all the info and even better call SpeedyPIN to inquire about how exactly you will place calls and how much you would pay. For example, the Globetrotter card displays a 1.5 cents/min rate from India, but if you click on the International Access Codes link you will find a 30 cents/min rate for India local or toll free access. This is the reason why the other card listed (MCI) has a much higher rate (this one includes local access).
To answer your question, yes these services work but, as I said you must know all the details before bying the card. Rates charged by the big names in the telecom industry are usually much higher.