I own both a Sterling conversion and a MR Stormtrooper blaster (I even used to have a looose MR I got for a nice price) and I can say the MR version is very cool, and in some ways comparable with the real deal. Regarding the price, you should only pay as much as you feel confortable with, but this should apply for everything in life.
The MR is full metal, and copies the Sterling pretty accurately, though being a bit idealized, but not more than many fan made E-11 I've seen. The scope has a nice targeting system on it, the trigger, selector switch and folding stock are all fixed and non-movable, and there's no cocking mechanism. It doesn't come with Hengstler or cylinders, but they can be added pretty easily. You can even replace the scope with a M38/M40/M19 if want to. There was a prototype MR that came with Hengstler and Cylinders, it is owned by a Rebelscum member:
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They all come with a cool mirror base, a cool COA and numbered plaque. Some MR E-11 blasters might have a crack where the back suppot for the blaster is, due to its weight.
You can see a comparison of my MR and Sterling below:
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