Things I liked: This gun feels sturdy and has a nice weight. The slide action feels much more durable than the MK23. It's pretty accurate and has a decent magazine capacity of 25 rounds. The gun looks good and is comfortable in small hands. I got this specifically to shoot with a friend who is using my MK23. The MK23 is a monster (size), but this gun is very comfortable to shoot.
Things I would have changed: Add a second magazine to the package and a better manual. The web site of the manufacturer, www.UmarexUSA.com doesn't even list any H&K models on their site.
What others should know: I really like this gun and will probably be in the market for a nice, metal, Gas Blow Back version soon. The biggest drawback to the spring version is that I cannot find a magazine for it anywhere. I would really like to have another back-up magaine or two without having to buy a whole new gun. It's really a shame that magazines are not available (even from the manufacturer's site). Otherwise, I'd rate this gun a solid 5 of 5 stars.