we have been using Terrafin for several years. We have found them very helpfull! Linking this with on board satelite would be awesome! I especially like the availability of the charts. Limitations are the satelite passes are on California time.
We used Terrafin a couple of years ago and did not renew. They make the decision as to whether to post the day's chart or not based on cloud cover, etc. Many times, the cover opens up in a spot of two and we can see surface detail on other charts but No-o-o, Terrafin doesn't post their chart.
We have found the Rutgers and Johns Hopkins charts as good as anyone's once you have a good many years of experience with them. While their depth contours and Lat/Lon may not be precise, they are consistent