I run esignal at the same time as OEC.
The data displayed on the oec depth of market is the same exact data as esignal.
I really don't care for the charting on oec so I use esignal, and also I use Quotetracker. QT is one of the best at charting, easy to use, and the very best staff to back up their product.
I see no difference on the DOM, even when things move fast, and esig.
OEC does not charge for the charting. It is included in the account you open.
So for free, it does the job.
I cannot speak for IB, but I can provide this feedback on oec.