Passive earplugs have always been my preference, they do the job well and have less to go wrong.
Currently from personal experience, Mercury are extremely poor with after-sales customer service when dealing with a fault on new passive earplugs. Sporadic responses to e-mails and contact via their web link at best, with the vast majority of them appearing to be ignored. This is a shame as I was happy with my previous Mercury earplugs taken before they moved premises.
I have now gone to Custom Fit Guards after numerous personal recommendations and to-date I have been very impressed with their communication and home visit impression taking.