Check each site on the UK Gambling Commission register, then read bonus terms...

https://high-wiki.win/index.php/BetNinja_says_it_has_an_installable_app_%E2%80%93_what_should_I_check_first%3F

Check each site on the UK Gambling Commission register, then read bonus terms closely: a 10x wagering cap can matter, but don’t assume it makes an offer good value