You are correct, there are two options for a Stealth Hitch on your 2021 Audi Q3. The Stealth Hitches Hidden Rack Receiver # 391AUDQ319 and the Stealth Hitches Hidden Trailer Hitch Receiver w/ Towing Kit # 391AUDQ319T.
Essentially the difference is that the Stealth Hitches Hidden Rack Receiver # 391AUDQ319 is only rated for use with hitch mounted accessories such as bike racks and cargo carriers. If you wanted to tow a trailer or anything else you would have to add the Towing Kit w/ Ball... view full answer...
I can understand why this is confusing! The Stealth hitches like the # 391AUDQ319 are a bit of a different animal than a conventional hitch, and the receiver that it comes with is designed only for carrying hitch mounted accessories like a bike rack. If you're going to want to tow with your 2020 Audi Q3, you'll instead want to use the # 391AUDQ319T which has a specially designed ball mount and 2" hitch ball that is designed for towing with the Stealth hitch. If you look at the notes for... view full answer...
We have not had a chance to install the Draw-Tite # 75218 on a 2015 Audi Q3 yet so I do not have the exact ground clearance measurements, but based on the two manufacturer provided installed photos I believe you are correct that it will give more ground clearance than the Curt # C13238.
If you are planning on towing with your Q3 you will also need a vehicle wiring harness # 119250KIT, and a hitch ball, ball mount, and hitch pin and clip which can all be found in the etrailer Ball Mount... view full answer...