I recently picked up an HK VP9 and figured I would post a small review for anyone who may be interested.
As a background, I am generally a big proponent of the M&P9 which is the primary pistol that I spend the most trigger time with, to the point that I have 2 set up identically. I generally run 8-10k rounds per year training with these pistols. I like Glock pistols as well but their ergos dont work for me which is why I prefer the M&P. I have found either to be equally reliable. I do love my 1911s but mine have become collection pieces that only come out for fun shoots or qualifications.
Size wise the VP9 is very similar to the M&P ( in between G17 & G19) with excellent ergonomics. The ergos are partially great because of the modularity of the grip. You can change backstraps like the M&P and Gen 4 Glocks, but it goes a step further with different side panels that allow the volume of the grip to be adjusted as well. It makes the grip possibilities much more likely to fit almost any hand. One thing that will take a little getting used to is the paddle (lever) type magazine release, particularly if you are used to push button style. After a couple of minutes you get used to it as it is placed well for easy manipulation, while being very difficult to accidentally release
Trigger is usually an issue with striker fired guns. The VP9 has possibly the nicest out of the box trigger that I have ever shot. It is miles better than the M&P (I use all APEX triggers) and significantly better than Glock, FN, SA, etc. That said it is a little bit long take up with a corresponding longer reset. It definitely takes getting used to. If you are a shooter that leaves your M&P or Glock Stock then you will love the VP9. Pull is an even 5lbs and nice and clean. At some point I will look into shortening up the trigger but it is nice enough that I have no plans short term.
Sights are std HK tritium 3 dot. I generally prefer a fiber optic or tritium/FO front and blank rear sight. This is just a preference of mine not a knock on the VP9. There is very little in the way of aftermarket HK sights so I wouldnt plan on changing them.
The VP9 has an interesting feature which is charging supports on the back of the slide. These are to help get an easy grip when charging the gun. They are very low profile and dont get in the way, but are actually kind of nice. If you dont like them they are easily removable.
Reliability and durability are tough to judge. As it is an HK I would expect durability to not ever be an issue, nor would I expect to have a reliability issue. I put 600 rds through mine last weekend. I shot a mix of Freedom, Federal, Fiocchi, and Winchester 115&124gr FMJ. I also ran some Hornady Critical Defense, Speer Gold Dot, Federal Hi-Shocks. Everything ran great, no issues at all.
Overall this is a great gun. I am not going as far as replacing my M&Ps at this time, but I like it enough to spend a good amount more time with it.