So far, I couldn't find any safe and legal place for margin trading besides Kraken.com
Is there any particular trustworthy place you could recommend?
I am not quite sure whether it is used actively in the USA or under what conditions it can be used, but I can recommend the FTX platform. One of the biggest advantages of this service that I have used and was very pleased with is that it offers the opportunity to trade with USD, not USDT. Moreover, the leverage service they provide can be increased up to the rate of x101. I prefer to use the FTX exchange because of its fast trading opportunity, high leverage, fast money deposit and withdrawals, high leverage, high volume and ease of use, and I can recommend you to use it here. I would also like to let you know that I have no responsibility in case of a possible problem, I just advised on your request.
The platform you mention doesn't accept American citizens from what I see and it's exactly what the original post was asking, a place for traders in The US.
So all the pros and cons don't matter to him/her
https://help.ftx.com/hc/en-us/articles/360042412652-Location-Restrictions-FTX does not onboard corporate accounts of entities located in, established in, or a resident of the United States of America, Cuba, Crimea and Sevastopol, Iran, Syria, or North Korea. FTX also does not onboard corporate accounts located in or a resident of Antigua or Barbuda.
FTX does not onboard personal accounts of current residents of the United States of America, Cuba, Crimea and Sevastopol, Iran, Syria, North Korea, or Antigua and Barbuda.