Also, gdax is a currency trading website. technically a currency trading platform with margin trading for daily trading so it's not really intended for buy and hold in your wallet investing like coinbase. That's why price is lower on gdax, because people theoretically will be using it and paying fees more often. This would be gdax way of giving day traders more incentive to use them rather than other day trading sites. Not too good to be true just intended originally for a different purpose but still usable for other purposes...like say an old piece of clothing that was meant to be worn but you can cut it up and use it as rags to clean instead. Not original purpose but it works!