I think Coinbase has actually done a great job managing GDAX and expanding it to the more "advanced" investor. GDAX now offers spread trading through its partnership with Trading Tech, along with futures trading. I've yet to dive too deeply into this but given the volatility we're seeing in both volume and prices, there's some huge opportunities in spread trading BTC and ETH, amongst others.

I wouldn't be surprised if we saw some above average spreads during this last month's sharp declines. Given that institutional investors haven't quite fully penetrated crypto yet, those spreads should be available for active investors.