I have never liked the concept of trading on centralised exchanges But I am still stuch with it as the Distributed exchanges are not yet ready, they don't have enough volumes or alt coins added. I did try Changelly initially but didn't see it through. Thanks to your post I will reconsider it again.
Yes those are makers, Changelly is a taker. Changelly compares prices on multiple exchanges and positions your order in smaller parts at the best available rate.
So even if there would be only decentralized market makers (replacing Bittrex and Polo), Changelly would still have it's use because it would stil check and execute the trade the lowers price level between the exchanges.