They are licensed and regulated by the UK Gambling Commission and have been in business since 2001. They offer a wide variety of gambling games, including sports betting, casino games, poker, and bingo. They also have a good reputation for customer service and security. In my opinion, 100% yes they can be trusted.
The term bet can be used in a few different ways, but generally means "agreed" or "okay". For example, if someone says "Wanna grab lunch later?" and the other person responds "Bet", it means they agree to the plan. Bet" can also be used as a response to confirm that a statement is true.