I have only put about 200 rounds through one, but to me it was nothing really special. I too like HK as a company, but for the price of the MR556 I would pass.
If you want a piston driven AR, you can find them for close to half of that price.
- It's made by HK
- It is not something that many people have
- It is accurate
- It is piston operated
- It is pricey...
- Doesn't really do anything that "cheaper" ARs don't
Have you put thought into getting a suppressor for the ARs that you already have?