I use PIA and never had an issue, don't have to download anything to use if I don't want to and it doesn't log.... not expense to have, I pay $39.95 USD yearly, less if I pay bi-annual.
IMO if you're doing creative work, go with the iMac. That 5k screen is perfect for anything from graphic design to video editing. But, if you're gaming, go with the custom PC. You'll have far better performance with the 1080ti, as it's designed for gaming. If you do light creative work but mostly game, the PC will still be the better choice. Plus you can upgrade and expand it easily in the future. VS the iMac, you're sorta stuck with what you bought. (You can upgrade the 2017 model's CPU and RAM but you'd void your warrantee)