Anyone Using Furuno GPS/SONAR COMBO 1670/1870 or 1971 + C-MAP 4D?

[Sharphooks]

Curious if anyone has experience with the C-Map 4D charts that you have to purchase for these units, specifically, the bathymetric part of the chart software package.

It’s an expensive nav add-on and I was wondering if the bathymetric part of the charts are worth the approx. $ 300 investment.

Thanks