I personally have OneCard, and it is used quite well. I don't order food much online, but many of my friends do and they always pay on Swiggy using OneCard CC.
I personally use OneCard for buying grocery from BigBasket as it gives flat 10% off on purchase of items above 1500 so it is beneficial for me in that case. Also one of knowns bought a Samsung phone off Samsung website and One Card was giving flat 2500 off.
I don't know how long those offers would last. But yeah One Card is useful. Though Zenith is much premium card to own as it comes with priority pass