1) Do you really believe in trustpilot reviews (in general)??? If so, then you are simply working with a misleading information; these reviews have a very, very limited relevance. For a valuable information you should search at sources like forums used by people that 1) are (relatively) unbiased and 2) know what they are talking about. (So for fintech opinions e.g. here 😉 )
2) I cannot fight for Yuh, as
– it's a relatively new project (AFAIK), so with a limited︀ track record;
– I can imagine quite well that there some problems can be induced︁ by a completely different nature of both institutions (SQ and PostFinance) that (in general) must︂ act togehter / cooperate somehow...
3) Nevertheless, SQ is a well-established trading platform, with history︃ and good reputation as well. And just for the record, if you possess their credit︄ card, they can issue a prepaid card to you, too. (Yes, they are not the︅ cheapest traders, possibly.)