If the OEM with software is $2250 and the 3rd party is $1200 I think I would go the OEM route - depending on what the software does. It is an extra $1k on a $50k car I could live with that. But I would be towing trailers a bit. If it was mostly for a bike rack I wouldn't bother.
I have an OEM towbar and tow module on my Touareg and am glad I do. The build quality of the bar is superb and perfectly matched to the chassis. The module does smart things such as disabling the rear parking sensors when the trailer is connected, and tells me if there's a problem with the lights on the trailer. Supposedly it does other mystery vehicle management stuff but not sure exactly what - possibly alters the braking or transmission parameters?