Navionics was updated last year. You now need a subscription to download maps. Without a downloaded map, the resolution is terrible. It's usable if all you need to do is to get to/from a port. But the bathymetry lines have like 0.2 nautical mile resolution, and the coastlines are so low res I usually can't recognize them anymore. Fortunately I downloaded an installer for the previous version when I was trying to install it on an Amazon Kindle HD (Navionics Boating HD wasn't available in the Amazon app store). So far it and downloading maps has continued to work without a subscription. It auto-updates every couple months to the crippled subscription version, and I have to revert it to the old version. But obviously that's not a problem when I'm out on the water.
If you're thinking of using an iPad with Navionics (or other navigation software), be forewarned. The WiFi-only iPads do not have GPS. You have to get a cellular-capable iPad to get GPS. It's also possible to link up a WiFi-only iPad with an external GPS receiver. And there are certain apps which let you link your phone's GPS with your iPad over Bluetooth. But if you're hoping for a standalone device for navigation and it has to be an iPad, then you must get a cellular-capable iPad. Most of the mid-grade and high-end Android tablets have GPS (the Amazon Kindles do not - which I discovered after I installed Navionics on mine).
I agree all the chartplotters and MFD models are needlessly confusing. But the pattern I eventually figured out was that the higher-end models simply add (1) a larger display, and (2) support for additional features like radar and networking. So if all you want is a chartplotter, the lowest-end models will probably serve you just fine. (I do a lot of fishing so I bought one of the higher end models, so I can't give you any suggestions for low-end models.)
- B&G, Lowrance, and Simrad are the same company - Navico. B&G is their line for sailing, Lowrance for freshwater fishing, Simrad for saltwater fishing (more ruggedly built). As best as I can tell, they all run the same software under the hood. The different brands just have some minor tweaks to the hardware and UI.
- Garmin is considered the Apple of chartplotters/fishfinders, with arguably the easiest to use interface. Garmin bought Navionics in 2018. They've said they'll keep the Navionics maps available for other brand chartplotters, but just be aware that they now control the primary aftermarket maps added to most chartplotters. One notable drawback is that (as of a year ago) their screen mirroring app was iPad-only. The other brands can mirror the display (for the models which support the feature) to Apple or Android devices. OTOH, their navigation plotting integration app for iPad is supposed to be the best in the business - plot your planned route in your house on your iPad, and when you get to your boat it auto-uploads it to your Garmin chartplotter (may not be available with all models).
- Raymarine in my experience had the best online support. They were able to answer some of my very technical questions while I was shopping. On top of it, they don't make it a secret that their plotters run on SoCs running Linux. In fact they'll even give you instructions on hacking the unit to do things like pulling out recorded course routes if the built-in UI feature fails. Also, looking around my marina, the vast majority of radar units I see are Raymarine.
- Furuno is the other major brand. It's very popular with commercial fishermen, but tends to be higher-end and more expensive. So I doubt you'll be considering any of their units.
- Humminbird is a freshwater fishing plotter company. They have a very small market share, and I don't think anyone other than freshwater fishermen consider them.
The other advantage of a standalone chartplotter is that they usually come with a rudimentary sonar unit. While you won't be making extensive use of the sonar if you're not fishing, it's still nice for getting real-time depth readings so you can always be sure there's enough water under the keel. (It'll also tell you water temp.)