I have both. The highlighted red and green that you can adjust for shallow water and say a depth you wish to target on Lakemaster is nice and pretty, but Lakemaster is way off on depths on most of our lakes in north Texas. Navionics is spot on so far as I can tell. If I only had one it would be navionics.

IMO one of the most important features on your Helix 10 is Autochart. And it won't work with Navionics.

What card do you have now? If it is an old or premium card or another brand you can buy and updates card and use your existing card to activate. Once activated, you will have a brand new Nav+ card just at a discounted price for being a prior customer. If you have an older Platinum card, you can call Navionics, tell them you want to update an old Platinum card(which the new ones you can just do online but due to the old cards size 2GB it wont hold all of the data) they will send you a new platinum card with 1 year of updates for the same price as updating a new one online $99. Then from there on out you will just be able to plug it into your computer and update.