First of all, I should make it clear that I'm a beta bester for PocketFMS, so you should bear that in mind when reading my answer
I would say that you should ask yourself what you want it to do for you. If it's simply to show you where you are on a map, then Air Nav Pro may be sufficient for you, and save you some money over the others on the software cost. (Not sure if you've already purchased the hardware or not). I haven't used air Nav Pro, but understand that it is very slow, and only shows airspace close to your current level. But I'm sure there are Air Nav Pro users here who can better comment.
If you want to use it to do some planning, then the data becomes much more important. You can always do your planning the traditional way (Chart etc, of course making sure that you update them by hand as amendments are published!) But if you want to use flight planning software, then you really need the data to be accurate.
If you want the GPS to show you where you are in relation to airspace, and to warn you if you are about to enter airspace, then you really really need the data to be accurate.
If you want to fly to foreign countries, then I think you'll find that having accurate data that you can trust a big advantage.
PocketFMS, has pretty much worldwide data, and all is included with the system. Metars/Tafs are also included, but so is advanced weather. Advanced Weather includes hour by hour forecast for the next 3 days, winds aloft, and rainfall radar (not for all regions, but all if available in Europe).
dp