To use the L5 really as a daily driver - especially in a business case - not one modern app will be available. The Debian base is ooooooold and o all apps in Debian.
And also no possibility to use with something like easyness Signal, Telegram, Geary ad more 
Are you talking about Geary or Epiphany browser ?
Geary, Epiphany is absolutely the same thing as Geary. Debian base too old on the L5. So without flatpak no use for me for the L5
Some worries (to me):
Absolutely correct, but the Geary delivered with PMOS is unusable. So I have the possibility to use an unusable but safe software or a stable running and usable flatpak Geary
Easy to decide what to use.
The problem is the old-old-old Linux base of the L5 and as long as this is not fixed from Purism there the need to use Flatpak apps would grow every day
I am not sure we will see Crimson in a foreseeable time
Pretty sure that you can download crimson for the Librem 5 right now - but it comes with caveats.
e.g. Crimson Experience
This is not a real usable Debian on the L5 I think. The issues in the actual build are enough 
If I make an upgrade I want to have newer features lik a working suspend and a smaller energy footprint FE. But there everyday I have more doubts about this to come
It is usable for me, but feel free to think whatever you want.
I could use if it is “better” tan the old Byzanium. But as I see FE the camera does not work. How about the Energy experience with Crimson? Suspend any better?
I would gladly try it, but it should as least work as with Byzantinum
Currently, I do not have the time to benchmark Crimson, so either wait around a week or flash it yourself.
And to note, for many people that would be:
then flash crimson. That way, if crimson is not to the person’s liking, there is an easy, clean restore point.
This will potentially cause the loss of any SMS/MMS messages that came in during the time that crimson was being run so if the purpose of running crimson is to see whether Geary works better or ensure that power consumption is not worse (including that suspend works) etc., it could be wise to disable receiving SMS/MMS messages temporarily.
Why nobody states clear what is with suspend, millipixel and geary in Crimson FE ?
The guys tested it must have some experience with this or has only a very small amount tested it now?
What about the Crimson installation if Crimson gets final? Could the testing instance be upgraded or mus we make a flash from the beginning?
I do not use any of them myself.
I do not know for the first two questions, and the latter for the last question.
It is “easy”
If I switch to Crimson and then finally Crimson will be stable and rolled out - can I update to the official release or have I the need to flash all from new and have to config all my settings from scratch?
I have no great desire to flash an early stage from Crimson which is running more worse and incomplete than Byzantinium. I hope somebody has tested Crimson out a bit an can report his experiences from a running and used L5 ?
Probably the latter, and I already report my Crimson experience in a dedicated thread.
Have read this, but no word about Suspend (energy consumption) and a working Cam ?
My expectation is that if you flash crimson now, it will be an in-place upgrade when crimson is final. However that’s a prediction about the future and hence can be wrong.
As already mentioned earlier, I do not use either of them, among other features.