The Kobra sight is the Russian equiv of the US Red Dot Sight - hence no zoom. I prefer it to the RDS, it's a slightly different aiming process. Rather than put the dot on their face, it's get them in the gap between the lines.
So you see what you are aiming at, rather than trying to keep at dot over what you are aiming at. It's small differnce I know, but it's about what you are comfortable with.
The Russian holo is poor compared to the US Holo. Mainly due to the fact it's fitted like a scope, rather than being a semi-open sight. As per RDS, Kobra and US Holo.
If you are gonna use a scope style sight use the Russian 3.4x, it has a "chevron" rectile like the US ACOG, but is slightly easier to use as it's a fraction less zoom. Stick it on the AN-94, sit close to your screen and go for head shots. MMmmmm, headshots!