We have the version that is made in Germany called the MR223, the only draw back is, it's receiver pins are offset by 6mm to meet German export laws, This mean you cannot swap your lower or upper receiver with another manufacture, but why would you really want to anyway!
The MR556a1 you can swap lower & uppers with other company's but keep in mind the barrel is not made by HK directly but Daniel Defense, last time i checked anyway. Also other parts are made by other companies to satisfy the "Made In America" lobbyist, which is cool.
Just buy the MR223 and you won't ever look back.