I think you've already subconsciously answered your own question:
For 1100 euros and looks incredible!No errors.
I dont mind the weight of the S5.
Yes, you want that instrument...
the s5 lmmmh and is significantly heavier
Although the S4 is "lighter" in weight, this S5 (nearly 13 kg) has five choirs in the treble (LMMMH) – has one extra M-choir. That's why it has 13 registers in the treble side (the S4 has only 11):
If you are young and don't mind the heavier weight of the accordion, you have made the right choice! This S5 will give you everything and on top of that, it even has the ability to imitate a musette. The lower M-voice was usually tuned to -8 cents, the upper M-voice (choir) to +24 cents - both outside the cassotto. It is the combination of the two that is very unique and many like it:
As for the "big", or "musette" tremolo - this one:
It has a different sound from the French classical musette because the middle M-voice (0-cent) is in a cassotto (the shaft dampens the higher partial frequences) and its tuning to the two remaining M-choirs is asymmetrical (as mentioned: ca. -8 cent and +24 cent). Therefore, the tremolo of this instrument has a different (and indeed unique, yet beautiful and gentle) sound than Italian, German or French instruments with symmetrically tuned tremolo.
On the other hand, its discant-disposition is excellent for Balkan music that, in addition to the separate M-voice in the cassotto, you also have a separate lower voice (M-choir; -8 cent - red arrow) at your disposal, both registers will be very useful for Balkan folklore:
My final conclusion: you made the right decision!
And… only a small warning: check the inside of the instrument, especially to make sure there is no corrosion on the reeds (they are Italian Tipo-a-mano reeds inside).
And don't worry that the bellows is attached with screws and not nails - that's how it was made back then, it's fine. That's original condition only...
Best regards, Vladimir
