By paying this site ofcouse you will get some amount of discount but there are more cons in this site than pros.
First
If you recieve a cashback in form of discount, you will not be able to utilise it easily form paying phone bills as the site always respond "try again later" so you end up with frustration after 5-6 trials.
Second
I have paid through mobikwik once on one of the famous site but I didnot like the product so I returned and the site initiated the refund through mobikwik.Received the amount in mobikwik wallet and when I tried to contact them to transfer the money in my account back, They have asked a 4% of charges to be deducted from the amount.Which is really irritating.So I highly avoid paying through this site as you cant do anything with the money remained in their wallet.Nor even you can pay the bills.Refer to first cons
Third
Their customer care service is also not good.