I got the pistol just the other day and have not shot it. I am not an experienced shooter.
I mounted a Delta Point Pro atop, something the Q5 mounting system makes idiot proof. The pistol points naturally and finding the big 7.5 MOA delta from a draw is way easier than I anticipated as a result. The only way to cowitness is to install accessory rear irons for the Delta and then find an appropriately tall front sight. Other pistol sized optics, as far as I know, do not have this option. The optic mounting method is pretty slick; however, the optic mounts considerably higher vis-à-vis a milled slide (though likely a bit lower than a dovetail mount and are much easier to switch out). PPQs already sit somewhat high in the hand compared to a Glock or CZ.
The pistol seems more front heavy than the PPQ 5 and it is indeed heavier overall by an ounce or two. It is still a featherweight pistol. The Q5 barrel has polygonal rifling; I think the PPQ 5 is land and groove. The Q5 irons are lightyears ahead of the PPQ’s and are overall pretty good—an adjustable black rear and a fiber front. Another significant difference is that the magazine release on the Q5 is considerably stiffer than the stock PPQ, ostensibly to address complaints of accidental magazine drops. The Q5 trigger is more or less identical to the PPQ. It comes with 3 magazines and has a nice case designed to accommodate the optic plates, associated tools and the Q5 with optic attached.
For about $100 more than the PPQ 5”, already a great firearm, the Q5 is a nice value. The extra magazine is welcome, and while I prefer a Dawson set to the stock Q5, nonetheless they no longer are a must purchase. The option to mount a variety of optic brands is great and is the strongest selling point over the PPQ. If optics are not important, there really isn't anything it does better than the long slide PPQ with aftermarket irons.