Sometimes I forget folks don't all live within access of a good range. Sorry about that. I would still drive a few hours to shoot the guns, though, as I find the SIGs and Hks to shoot very differently in my hands.
Operationally, my SIGs and my Hk P2000 are almost the same. TDA with decocker, no safety. But they do handle and feel differently in recoil, and friends that have shot them but don't shoot regularly often strongly prefer one to the other.
But to answer some of your questions and further your research, here's my thought on safeties: they're fine if all your guns have the same safety system.
I carried a 1911 for years, and only shot 1911's. I never had problems wiping the safety, for, of course, that's all I had and trained with. Over the years, however, I became less than enamored with 3" 1911's (my choice for CCW) and the SAO trigger system. As a CCW'r, I began to look to TDA (DA/SA) and DAO systems, as I want to do all I can to prevent sending a round down the pipe unless I *really* need to. Some of my 1911's had a scary quick break.
I sold all but one 1911 and moved to TDA SIGs. After a good bit of range time, I feel very good about that move. I am much more comfortable with the DA first shot, and I really like having a decocker. Plus, the guns shoot very well in my hands, are easy to clean, eat anything I feed them, and seem quite durable.
I then decided I'd like to investigate a poly pistol for summertime carry, when I didn't feel like pocket carrying one of my j-frames. I decided on a Hk, and after trying out the USPc and P2000 at the range, settled on the P2000. I bought the V3 as it's TDA with a decocker, similar to my SIGs. I like the Hk a lot (even the mag release and nonstandard decocker location), and have enjoyed my time with it so far, even though it's not yet as accurate in my hands as my SIGs. Just a familiarity thing.
With respect to familiarity: I would not have carried the USPc with the safety. Why? Because I have moved so far from manual safeties, that I could not reliably count on myself to wipe it in a stressful situation. I purposely sought out the Hk variants without a manual safety (well, the P2000 has none, anyway, and you can get the USP's without them). If it's all you train with, I find no problems with the choice of a safety.
Is it a benefit? Only you can decide. I would not carry a SAO without one (of course!). If you plan on carrying in a pocket without a holster, I wouldn't carry a TDA without one. But for a regular TDA carried in a holster; I don't see them as a benefit, only one more thing to remember. I do believe training can overcome that, but with a TDA it's just not necessary, IMO.
I hope that rambling helps
As an aside: the P2000 has a standard Picatinny rail. I believe all future Hk's will also have a standard rail.
