I've been using xScope since late 2015. I haven't used PixelSnap, but looked at it and was considering buying as PixelSnap's magic "snappable" features are pretty cool. xScope is $50 and PixelSnap is $40 to install on 1 Mac, but $70 to install on 2 Macs and $160 to install on 5 Macs. I have two laptops and a desktop and appreciate licenses to install on my personal Macs for non-simultaneous use, and xScope has this through the App Store purchase.

xScope also offers other tools. I use Rulers, Loupe, Guides, and Crosshair and they are all nice and work as expected.

https://xscopeapp.com/features

I have used xScope ever since it was released and was one of my must-have tool. In the last 5+ years, my need for design tools have reduced a lot. I subscribed to SetApp and PixelSnap is part of it. I just have it around for fun and a nostalgic feeling that I get out of doing “designs”.

If you already have xScope, it should serve the purpose pretty well and much more. PixelSnap is tad “modern” in a sense (I don’t know how to explain that one). If I remember correctly, xScope has other tools that should be handy for a dedicated designers.