I've never heard of this version and it's likely that the packaging is a knock-off, but that the model is real. It's not American, you can tell by how the stats are given in metric first. The stats are also an almost exact match with the real MK1 - 340 grams weight, 49.5 cm length, range in the low 30s. The genuine MK1 is marked with 50ft, which it never achieves, but is a reliable identifier box-wise. The only way to know for sure is to open one of them and compare against the a real one. Like I said before, it's probably a genuine SS 50 that got re-boxed and re-marketed. It's circumspect if there's no brand or maker on the box anywhere.
It would likely be worth more if it's not an actual SS 50, because the SS 50 is a mediocre soaker in performance. It was the king of its era, but is now only a notch above the Nerf Super Soaker series. Hasbro has actually started making piston trigger designs again, in essence regressing all the way back to the 50, and beyond that with their battery powered models. Water gun value is heavily dependent on how powerful the gun is, not just how rare it is. You may have something that is extremely rare, and thus may be able to fetch a good amount if you can find the right collector. That is the key to these kinds of things, where the model is unique, but lacks performance. I'm not sure if here or Ebay are the right places to list it. You need to find a person who doesn't care if it sucks or even still works. I can refer you to a couple people who might be interested in buying that, but you'll have to be willing to ship internationally and/or be willing to negotiate with very informed collectors. We're not the same people who go nuts on Ebay, nobody knows who they are.
Be really careful if you go the Ebay route, because you have to know 100% if it's genuine or not before choosing keywords and writing a description. If it's not Larami-boxed, you can't call it an SS 50 even if that's what it turns out to be inside the box, unless you sell it without the box. We go on there and look for fake soakers to report daily - some models are worth so much that it's painful to watch all those poor n00b bidders get ripped off.
So, your find is definitely cool, and definitely worth further discussion. I'm not sure if it's worth money without seeing what's inside.
I opened one of them up, and modded it before you commented, thinking that it was fake. However, I took some pics of it before I modded it. One of the most interesting things is that the handle is detachable, and Im not sure if this confirms any suspicions (making it real or fake).

Close-up of tank

Trigger design also seems to be different than one pictured on top. I opened it up and it uses no springs at all. It is a black, metal piece that pushes it down, and there is a tube that goes under it. When the trigger is pulled, a pin comes off of the tubing, letting the air come out. Unfortunately, I didn't get any pics of this before modding it, and I cannot replicate it to show how it worked. Also, it shoots a good 30 ft (advertised on the box).

I am willing to ship internationally, if we can get that far and if the item is truly an Mk1.
Thanks for your input!
Probably lurking somewhere...