Hello Karthik
Yes, this agency belongs to SBB, the Swiss Federal Railways company. It is official and trustful.
But, before you purchase tickets, draft your itinerary (bases, what to visit, etc.). Purchasing tickets should be the last step of your planning; we have seen people here who purchased tickets and later realised, there would have been a better offer that would cover the entire trip and not only a single mountain excursion.
You are welcome to post your itinerary for Switzerland here, so we can give advice on the most economic tickets for your trip.
Kind regards,
Roland