DBR -> Daily Burn Rate bro .. Instead of taking the whole topup amount as intial stage (upfront) .. They take in Daily basis .. Ex) topup cost is 45/m means they wont take 45rs as a first day of activation .. They take 1.50/day basis for 30 days ..
And some DBR topup's dont have lock in period (30 days) also ie) we can act today and deact tommrow ..
It looks like a 30 day offer. But Airtel has screwed up the dbr value of this offer as it shows 3 paisa per day which may be applied after 30 days. Add at your own risk. But looks safe.