I do, I own both the P30 and P30L my main shooting buddy's only HK is a USP Combat Competition.
The Combat Competition trigger is awesome, it is much better then the P30's. Yes the mag capacity is also great. If I were in the market for a USP that is the one I would buy (especially if it were available in .45).
The P30's feel much better in the hand, the P30 is smaller therefore easier to conceal.
What is your intended use?