I prefer using a BookMyForex forex card as the card is based on interbank rates with zero forex markup. I have used a Niyo card as well and even though they also claim to offer zero makeup fee, I feel they are misleading as their rates were still at least 1% higher than the BookMyForex card.
Also, when I reload my BookMyForex card before traveling, the rate gets locked in immediately.
But when I was using Niyo SBM cards earlier, before they were banned, the currency rates were unclear to me. Sometimes my account was debited many hours after the transaction had been completed. Even though my card would be charged with the exchange rate on the day, I think real settlement used to occur two to three days later, and most of the time, this new exchange rate was much higher. Personally, I did not enjoy using the Niyo card.