Hmm, that's quite high just for 21 days but if it's the amount that it shows for staking it, then that's considerably a steal for you. I was just checking some rates and apy from mycointainer and I think it's justifiable as to why Binance got that high percentage and as well as I've checked also some other platforms like Abra but it has a lower apy and only a few supported cryptos and bnb not yet there from their pool for staking. You've got various choices for each platform so take your time and DYOR for you to have that confidence where you'll delegate or stake it.