Read the all-in cost, not the expense ratio. The fee is the sticker price. The bid-ask spread, any brokerage, the demat charge and the gap to the ETF's fair value are the rest of the bill.

The fee recurs, the spread repeats. An expense ratio is charged once a year on what you hold. A spread is charged every time you buy. A monthly SIP of small amounts can pay more in spreads than it saves on fee.

Match the vehicle to how you buy. A one-time lump sum over a long horizon favours the low-fee ETF, the spread is paid once and the saving compounds. A monthly SIP, no demat, set and forget, usually favours the index fund.