I currently have both a helix 5 and 7. The 7 has GPS chirp and down image, the five is the same less GPS.
GPS can range from mandatory if you fish big water like I do that is reefy and big and complex enough to be able to get lost. Some of the places I go are good places to die if you don't know where you are. That's aside from being very expensive if you find a reef Most of my fishing is in places that GPS doesn't matter much.
The Helix units do not produce as clean of hooks as other units, but they will show small walleyes belly to the bottom, they just look different. The down image sonar is an absolute must IMO. It provides an outstanding view of what is down there. The conventional sonar running in split screen with the down image provides way more information and it is way more useful than either alone. For instance, a fish sitting in a feeding station at the top of a big weed might only show up as a little dot above the weed in down image while the weed is very well defined.. The fish can be well defined in conventional sonar and the weed much more abstract. Trees, rocks, brush, junk are all well defined in DI sonar.
If you do not fish big water without landmarks and that has reefs i'd consider whether I needed GPS. Fishing something like the great lakes which while not so reefy have other factors like locating fish again or like Superior where warm wet air can drift over the lake and fog you in within minutes can make GPS mandatory. Most of the lakes I fish are smallish, under 3000 acres. That to me does not mandate GPS.