I would have to disagree with you in that its an advantage to have DMA. When trading a derivative i prefer having the sythetic market provided by CMC rather than the DMA by IG.
In a synthetic market like that provided bye CMC you can set a stop loss while in a DMA platform you can't. This is a critical difference especially when trading CFD's when your positions are leveraged. its great when things are going well but when things go badly just a little it can really blow out.
Also i am not limited by the order flow as i am on a DMA platform. If there are only 10 shares available at the price i want on a DMA platform i can only buy 10 shares. On a synthetic model like CMC i can buy 100,000 shares, and becuase its a 'made up' market if i want to sell 100,000 shares i can sell them instantly. I do not have to wait to wait till there are enough people wanting to buy 100,000 shares to get out.
its all very complicated. There are a few books and recourses out there that explains the difference, advantages, disadvanges and how to use them to your advantage out there. the best i have found is from Guppytraders.com. Daryl Guppy really knows his stuff.