PB the PPQ M1 5" you referenced is nothing more than a PPQ M2 5"......they're the same gun, using the same upper (slide/barrel) the frame internals are the same (trigger bar, sear housing, etc.). The only difference in the M2 and M1 versions is the magazine release, the M2 has a button, the M1 has a paddle. Other n that, they're exactly the same.
Heck even the 4" Q's use the exact same frame and internals.
Only thing different about the gun you referenced is the paddles.
Now, if you already have a PPQ M1 4" or a P99 or P99C, it'd be wise to go with a 5" paddle as opposed to a 5" button. All PPQ's with a paddle and most/all P99's and P99C's will be able to use the same magazine.
If you go with a 5" button gun, you up da creek when it comes to trying to share magazines with its paddle buddies.
As for the lightening holes in the slide, Balance covered that. They're just lightening holes....the barrel is not ported.
Is that enough, or do you have any additional questions?