I use MyTrack data feed with Sierra Charts. I have feeds for the STOXX, UK Equities and the ES.
Live cash prices for the FTSE and DJI are available free of charge with the Silver (live) plan. Prices are reasonable, however, they do have regular problems with their STOXX feed and as they are US based getting a response out of them at UK opening time is difficult. You need to use Channel 12 on chat and they will pass a message on.
Because of the regular outages on STOXX I now run two copies of Sierra Charts, one using the IB (Interactive Brokers) data feed and one with Mytrack. If money were shorter than it is I would consider reducing my MyTrack subs to the Basic Plan (delayed) and using that for historical charts with the IB feed as the live feed.
Overall I'm pretty satisfied with it, a good basic service at a fair price.