I have one in 9mm and love it.
Now, I prev had a fullsize USP, but the grip was too big for my hands. The compact grip is smaller. However, it took me a while to stop shooting low with the gun.
I don't have this problem with any other gun - so at first, I thought the sights were off. I finally sandbagged the gun - and it was right on target. So, I knew it was me.
Whenever I let someone new shoot my USPc, they have the same issue. For whatever reason - it is very easy to tilt the gun as you pull the trigger.
It took me 800-1000 shots to shot doing this.
I have nearly 4000 rounds thru the gun now. I shoot it pretty well. But, it took time to get over that. So if ya start out shooting low - U can beat it if you practice.
As for the Equinox - I think that has a 4" barrel, right? The USPc is sub 4" - so that means a shorter sight radius...
Personally, I'd still rather have the HK.
I think the GG&G rail is the best - but it is the more expensive. As for lights - The TRL 1 is nice. And if ya want a laser on the light - the TRL2. U WILL need a rail before you can use typical lights, however. Otherwise U are stuck with super expensive HK only lights and lasers.