I have used both DAS and IB TWS. I used DAS for a few months and thought it was great. I went back to TWS to save money and I am able to trade more or less the same way I was on DAS, it's just a bit more awkward with the charts and Level 2. I combine it with TOS which I use just for charting.
For me, it's worth it for now to save the money in my monthly budget, but I'll get back to DAS at some point in the future.