Halti dog collar how safe are these collars?

ive just bought a halti dog collar and have been really pleased with the results. but today i was walking my dog and 2 dogs came from nowhere and they both went for him which resulted with my dog trying to defend himself. luckily the others dogs owner got his dogs back under control but in all the chaos my dogs halti safety strap which clips to his main collar as security actually unclipped itself and although he was still attached to the lead im now im wary about how strong these collars actually are has anybody else experienced this