I want to buy the suction cup for the mount because I'd prefer not to have the adhesive on my windshield.

This is a mistake. Adhesive pads are a lot less work, and simpler, and don't lose suction for no reason. Heat/Cold causes suction mounts to fall, eventually leading to the dashcam power port bending and no longer powering the dash cam, takes a while, but very annoying when it does.

the SG one has GPS built in and not mounted

No A119 has GPS built in it, it is always an optional mount.

Also, why is Spy Tec cheaper?

• This one is a A119S v2 No GPS ($90 USD).

• This one is a A119SG v2 with GPS ($100 USD) (what ever the hell the G stands for). + a 90 degree adapter for some reason (most would use GPS mount)

With GPS, with out GPS $10 USD difference, sounds about right.

What about this one: https://www.amazon.com/dp/B01NAERFRT/ref=dp_cerb_2 and this one: https://www.amazon.com/VIOFO-A119SG-GPS-miniUSB-Adapter/dp/B01MS4L9N7/ref=sr_1_1?s=electronics&ie=UTF8&qid=1525629908&sr=1-1&keywords=a119sg

Question about the last one: I know G means GPS, but why do they add it to the model number when other listings just include a GPS mount? This one says the same I want to buy the suction cup for the mount because I'd prefer not to have the adhesive on my windshield. But you can't use the GPS mount with the suction cup mount. I was hoping the SG one has GPS built in and not mounted, but judging by the listing it doesn't seem that way

Also, why is Spy Tec cheaper?