It shouldn't really be a surprise if you're into AK's but the Russians have produced a number of newer designs for the AK74 than just the older PSO/POSP series optics that we are familiar with. During the past twenty odd years they  have built a few dedicated 5.45 optics which have modern features and interesting concepts. While NPZ has been making some high tech and interesting optics, BelOMO has seemed to stay a little more traditional with their designs, at least with what we have available in the US. Some of their prototype optics are extremely interesting. Many of the BelOMO concepts seem to be aimed at securing military contracts and because of that there are a few prototype models that have made their way to the USA that are not in serial production.

Note that other than the similar Zeiss ZFK there are no known versions of the PSO or POSP that are calibrated in 5.45x39. There are ways to use these optics with AK74 type rifles but none that are designed specifically for them.

Being a 5.45 buff I've picked up a few of the dedicated military style 5.45 optics and figured I'd put out some observations and theories along with some hands on experiences.

Originally there were four main optic types calibrated specifically for the 5.45x39 round, but around 2013 BelOMO introduced the PO4x24P2, and recently in 2016 the amazing PO 4x17 was available in the US

(Note that while I list 1P29 as a dedicated 5.45 optic it is actually cammed for various calibers and can be used with the SVD, RPK and PKM among others. Likewise PO 4x24P has a 7.62x39 version as well, and PO 3.5x21P comes in 5.45 and 7.62x39 as well as probably one version of heavy machine gun)

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After many many years and lots of rounds down range, in my opinion the best all around 5.45x39 optics are: (in order)

PO 4x17 (AK74 reticule)
1P78 Kashtan
PO4x24P2 (AK74 reticule)

Po 4x17 is better suited for civilian activities, but Kashtan is going to be a tougher built optic (and has also been formally adopted by the Russian Army and VDV airborne units).

The only practical issue with Kashtan is that in order for the BDC to work you must use the 400m zero principle, which can make this optic trickier to use in civilian settings. For real world shooting against full-size or half-size silhouettes the 400m zero is very practical and quite effective, but it is not optimized for shooting small targets for fun. This makes it great for combat but not as easy for civilian shooting. Since the 400m zero equates to about a 10 inch difference between point of aim and point of impact at 100m, you can see it can be harder to hit something like a clay pigeon or coke can at those distances.

By contrast the reticule pattern of the BelOMO series AK74 optics is extremely effective and very simple. The boresight cross gives you point of aim = point of impact at 100m, making it very easy to shoot any size target. For the AK74 there are range marks from 100m all the way to 1000m for each 100m increment which gives you a consistent point of aim and sight picture for each target no matter how large or how small.

It is hard to find a better reticule pattern, but it is busier than Kashtan and not quite as fast compared the 400m zero

PO 4x24 is BelOMO's equivalent of Kashtan and uses the same AK74 reticule as PO 3.5x21P and PO 4x17, which makes it on par with Kashtan.

All around PO 4x17 is the most useful and versatile optic of the three. It is very lightweight, has a highly effective reticule and can be mounted on almost any rifle because of it's picatinny clamp. To me this is a must have optic for the AK74 or 223 / AK101 owner. Kashtan is highly collectible and a very fine optic indeed, but for the average shooter PO 4x17 will be the better choice

If you are a civilian and can only pick one I would recommend PO 4x17 with the RS Regulate side mount, or a different quality US or Russian mount.

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NPZ

1P78 Kashtan - Russian modern issue for AK74M and RPK74

(Includes 7.62x39 versions as well)

Classic 1P78 Kashan (top)
The new and ultra rare Picatinny Kashtan 1P (middle)
and the Picatinny Kashtan P1 (bottom)

NPZ
1P29 - Soviet copy of British Trilux/SUIT

BelOMO
PO 3.5x21P - 3.5x magnification with extremely wide field of view 

BelOMO
PO4x24P2

East German
Zeiss ZFK 4x45 - Former DDR cold war scope similar to the PSO-1

PO 4x17 on RS Regulate mount

I have not personally heard of a PSO or POSP type optic calibrated for 5.45x39, but it shouldn't be difficult to use any of them with a 400m zero as long you realize the turrets and additional chevrons won't compensate for bullet drop.

In a pinch POSP optics will work just fine as long as the proper AK or universal mount is used (SVD mounts do NOT slide on from the front and even though they may fit they will not hold zero unless by pure luck)

Top left: ZFK on SLR105 and PO 3.5x21P on AKSU
Top right: 1P29 on SGL31 and 1P78 on SGL31