Just picked up an SLR 107 FR..... Wanting a side rail mounted optic for some authenticity.

What optics would you choose? Are they worth it? Should I just go with a top rail and separate optic like an Eotech or Aimpoint?

Depends on what you want to do with it; personally, I like the Rakurs and Obzor.
Take a look here at TX Zen's site, he does an excellent job of covering just about every available optic and mount:
http://russianoptics.net/

My favorites in order of what I think are the best:

Magnified:
1P78 Kashtan
PO4x24P2

Collimator:
1P76 Rakurz
1P63 Obzor

Red Dot:
PK01-VS
PK-A Venezuela
Kobra

Side Rail for Western Optics:
NPZ and Alpha
RS Regulate

I've used a variety of optic combinations over the years and with the right mount virtually anything is possible so don't be limited to my list. A big factor in my choices are ease of use and how difficult they are to get used to (since a common complaint about Russian optics is that they are too tall or too offset compared to Western designs). I'm a fan of magnified optics and collimators over red dots personally which is why I like Obzor and Rakurs so much.




Z