Hi Mobbos.
I come at this parallel, but a bit differently from you.
I have two tablets with Navionics and C Maps plus paper charts.
The most expensive of these are definitely charts.
If you want to upgrade your nav system, again charts are the most expensive way to go.
Navionics is a one time purchase that can be downloaded onto two devices. This gives you redundancy if one devise fails.
The upgrades that they charge for are not absolutely necessary, but you can opt for them every few years as an option.
Nobody that I know upgrades their charts every few years, because of the cost.
As for safety.
Old charts scanned and stitched together would be the worst choice.
Old charts do not show new features. I am using charts that have so many things missing it is a joke.
However, I find many features in even old paper charts useful
For coastal sailing Navionics with upgraded every two years or so would be the safest way to go.
Navionics without the upgrades would still be safer than old charts.
My C Map has not been upgraded for almost 10 years and I bought my Navionics last year (old tablet left in the cockpit in the rain and smart phone died). I can't really see any difference between the 10 year old system and the new system, so am not so fussed about upgrading and paying for that service.
Any memory map CD will be old and you would still have to pay for it.
I wonder how much you would actually save, going for an old MM CD instead of a new Navionics install.
Lastly, as you mentioned the 2.6 star rating in the App store probably relates to pricing.
Buyers want cheap, but then moan when the upgrades come at a cost.
We all have choices
gary