Thanks for the replies, discussion and links. If I correctly understand:
*there is an overall reason about being regulated by swiss authority, and I agree it is better to have arbitration in the country where you live.
*It seems that for the mentioned brokers, the invested assets are segregated from the broker, then in case of broker bankruptcy the assets should be recovered by the client. In the case of DEGIRO this is not a personal account but an omnibus account (recovering assets might be a bit harder in this case?)
*In case of fraudulent behavior of the broker, such as money not invested or assets not properly segregated, EU regulated brokers are insured up to 20k, IB should be insured by US law (250k if I correctly understood). I am still not sure if, for the Swiss Brokers, the 100k ensured by FINMA regulation is an insurance for cash account (then a protection layer against the broker bankruptcy) or a protection against fraudulent behavior (as for the 20k for EU regulated brokers). In the first case would be the dane as for EU banks.