if 50000 identical triggers fire at the same time trying to buy the same stock with market orders they're going to get a bad deal, and people selling are going to clean up
It's certainly not illegal for me to do it, if you happen to tell me your stop loss orders over beers, or if I predict people's stop loss orders using public information and/or a sophisticated model.
So which side of the line is Trigger on? They don't seem to be a broker, exchange, or fiduciary, and they wouldn't be getting the relevant information from those sources.
"The User acknowledges and agrees that upon posting or transmitting information [...] on the APP, the User assigns to the Company [...] all rights, interest and title in and to such information"
If you want to manage your money through a tech startup, I suggest choosing one that is a broker and/or has a fiduciary responsibility to you!