Is HDFC Regalia useful ?

Hdfc debit is good enough for most things

If you are not travelling frequently, then it is not useful. It is better to have HDFC Millennia CC in that case

Apart from flight discount and lounge access. I don't find anything special

Most credit card become useless after a while. You better stick with debit / UPI. Its frustrating to cancel cards and service these days are being slow and unresponsive

Lol, no