2ndfan, I couldn't agree more about the external safety. Both my HK .40's, the USP .40 C and P2000 SK .40 have the LEM action with no safety, but since the hammer remains down, I can still carry chambered in either IWB or a pocket holster. I even removed the button safety from my Remington 870 Express Magnum 12guage. It is a pistol-grip home defense weapon that does not get stored with a chambered round (since I previously lived in Chicago and it was the closest thing to a handgun I could legally own). If I had a reason for a safety, like being stealthy in a war zone or hunting where chambering a round would give away your location or frighten deer, I would definitely use them but it still wouldn't prompt me to leave anything chambered and cocked when I was not preparing to fire it.
From your last message, I know you have a USP. My first HK was the USP because it was what my father used as his service pistol while being an FFDO commercial airline pilot....and HK had a deal where the pilot could buy one privately from the factory for $495, complete with tritium night sights and an extra magazine. My first impression to the SK was that it seemed too much of a compromise in order to be a sub compact. It just felt a little too thin and light when compared to the USP C. After much research, I bought it and have never looked back. Exactly as reliable as the USP and significantly smaller. The very best part is that the high capacity magazines from your USP will fit into the SK's. This extends the handle with the help of an HK X-Grip spacer and allows, in the case of the .40, it to increase the pistol's capacity from 9+1 to 12+1. I carry with the 9rnd mag and have extra 12 round mags loaded up as spares in my gun safe or in my pocket, if I ever feel the need to have more than one one.
To make a long story slightly shorter, don't let the small size or thinner slide fool you into thinking of th SK as a back-up gun. It is FULLY functional, fully reliable and as accurate as my USP.