Instarem's ~1.8% spread applies only if charged to linked credit cards. It does not apply when charged to the wallet balance. Try it. My experience is that the spread for wallet spend is roughly in line with Revolut, Trust, etc.There is no point in using Amaze for wallet spend if someone doesn't mind using a few cards.
You get 1% cashback in points, but you will already be out 1.8% from Instarem's spread, and have to deal with Mastercard's lousy FX rate.