I would expect any vignetting to only be a major issue at the wide angle end of the range.
Please don't expect too much from this, I have a feeling it will be a disappointment (on any DSLR quality lens/camera);
low contrast and prone to flare without the 'extra' lens hood
soft (their website says 260 lines/mm, I'm not sure how that equates to the figures on most lens reviews sites, since they give numbers in the range of 1500 - 2500)
softer still towards the edges of the image
it may well also cause colour fringing towards the edges
it may also give barrel or pincushion distortion
If you attach this to the front of your lens while away, make sure you have a means to grasp the thread adaptor, I have a feeling it may get stuck on something - because you'll need to do it up tight to support the weight without wobble.
Personally, I'd be careful in use - when your 50-200mm is fully extended, the extra weight, unsupported, might be a problem (I have no experience of Samsung build quality), but regardless of that, if the extra length hits something as you turn to get a shot behind you
Have I put you off yet?
Sorry, I perhaps shouldn't, but I wouldn't buy one.
To solve this focal length problem, I recently bought a whole new camera (Nikon P510), but that's not without quality and AF issues - and not as cheap as this Raynox device.