I've been using OpenBSD on my firewall for ages, but the fact that patches are only distributed in source form is a giant giant hassle. I understand the reasons for that but it's a level of inconvenience that I find unbearable today. On Debian it's just "apt-get upgrade". On OpenBSD it's so more difficult that I usually end just not patching it at all.
To add to Gracana's comment. M:Tier provides openup tool which will update your base system and packages to match -stable. That way you don't have to patch and compile your kernel yourself.
For trustworthiness of M:Tier, several project developers are employed by M:Tier.