@cryptographic,
I never heard this before! I am using Bittrex, Poloniex (Sometimes) and Binance (Sometimes) as exchanges, but never heard about GDAX until I read this article! Then I checked their web site and found these few features. Specially they are same as Coinbase, that means we can trust their service than others.
Here what I found via GDAX web page:

• Trusted and Secure
  We undergo regular IT security and financial audits. In addition, 98% of customer digital assets are stored entirely offline.

• We are Insured
  All digital assets held in online storage are fully insured. All USD balances are covered by FDIC insurance, up to a maximum of $250,000 per customer.

• Backed by Top Investors
  Our investors include the New York Stock Exchange, Andreessen Horowitz, Union Square Ventures, and more.

• 0% Maker Fees
  GDAX offers no fees on maker trades and offers volume-based discounts on all taker fees, going as low as 0.1%. See our fee structure here.

It seems like they are doing a professional business as Coinbase do! But again it's a problem to me to join them :/ Not supporting to world wide! Actually it's a very bad news for people who are out of US, EURO clusters!
Thanks for sharing this update and wish one day they allow us to use their services!

Cheers~