The original HS 2000 was designed as a 9mm service pistol with the resources of a national government, not exactly a powerhouse, but still with more resources than any private company except maybe GM or Toyota. I think we can assume thay they tested the design. That applies to the 9mm, I am leary of handguns in calibers for which they were not originally designed. Putting a .40 on a 9mm frame reminds me of a friend's Ford Maverick with a 302 V8. Tight fit.
Mine is a Sub 9 and I am very happy with it. As you noticed, the grip is very comfortable, it is easy to strip, shoots good and is either ugly or tactical, depending on your taste. It seems to be one of the smallest handguns with a light rail. Beretta 92 mags fit with a little modification to the hole for the mag catch. BATF has stated that as long as the mag still works in a Beretta, it is legal to use B92 prebans in an XD. Also, XD forty mags can be used as 9mm hicaps with a little tweaking. Same rules apply. The steel parts seem to be blue steel, which means that they will rust. I have not decided if the reported problems are because of an inferior finish or shooters who are used to the bullet proof finish on Glocks, time will tell.
There are now a number of holsters for it, I just ordered an Uncle Mike's kydex paddle and mag carrier from Ultimate Outdoors, if I remember, I will post my impressions when I get them.