Cyanogenmod Unofficial and custom kernel I am new to cyanogen OS and using cyanogenmod unofficial from xda for my xiaomi. Why, it is said unofficial and is there any official release available for xiaomi from cyanogen. Also, I am trying to use a different kernel(camera is not working with built-in kernel ). Whether I get updates, as the kernel is different? What are the specifications for a good kernel, And about security? Please give me, suggestions.
Availability of official CM builds for MI devices isn't guaranteed (see note at the end) because the individual maintainers usually put bug fixing at priority and keep other factors (e.g. enforcing SELinux) hanging, some of which are required by CM. This is the same for almost all devices - who doesn't want a fully functional ROM before anything else?

As long as the build itself works fine, the only things you need to worry about it are 1) what extras are added in the build (e.g. themes, apps favored by the developer) and 2) how often it's updated (again, largely depends on the developer).

As for the kernel... When the issue isn't resolved in the original build, it's rare that a custom kernel can remedy that (or why wouldn't the developer of the original build merge it?). You will get kernel updates separately from the kernel developer - flash every update manually. Also, every time the ROM itself gets updated, the custom kernel will be overwritten, so you need to flash the kernel at that point, too. Talking about security, if you could trust the dev of your CM build, there's no reason you can't trust the dev of the kernel - they're on the same tier and are equally likely to compromise your security.

For the last part, IMO, a good kernel combines stability, performance (e.g. overclocking and opt flags) and battery life (e.g. underclocking, undervolting). All other features are just icing on the cake.

To others: feel free to comment and point out missing/faulty contents!

Note: Official Lineage OS 14.1 Nougat ROM is available for some MI devices.(Redmi 1s, Mi3,Mi4,Mi5,MIMAX,Redmi3/Prime, Redmi Note3)