Again, we haven't done any recent detailed research on that, but in a nutshell I believe there are five religions that are allowed in Eritrea. All other religions are banned. Those who practise those religions are arrested and often tortured and told to denounce their faith. There have been a number of stories about Jehovah's Witnesses, for example, who have been tortured. The rest have been tortured solely because they refuse to renounce their faith. That's a huge concern, obviously.
Those individuals who belong to religions that don't want to participate in national service are not given the right to opt out.