Stuart,
With certain exceptions, the car manufacturer will source the tow-bar from one of the specialist manufacturers: Names that come to mind include; Bosal, Westfalia, Brink, Witter, and others.
Then companies like Towsure and EECO in the UK who produce tow-bars for after-market fitting.
Now that type approval applying to tow-bars, they should all be dimensionally identical and built to a certain standard. What sets each tow-bar manufacturer apart is the items not covered by the TA process: Specifically the quality of the steel used, the quality and checking of the welding and fabrication, and the surface coating / rust prevention.
Unfortunately much of this information is unavailable to people outside the industry, but Bosal and Westfalia will probably feature on most German designed cars (and Opel / Vauxhall)
The other part of the tow-bar is the electrical wiring package, and you need to find this out too: A dedicated harness costs more, but simply plugs into an existing socket; a relay isolation kit is cheaper but takes hours to install - taking the signals from the existing wiring and drawing power from a separate circuit; and then there are the scotchlock cowboys.
Summary:
The Vauxhall (Opel) tow-bar won't be a Towsure model, but I know what you mean - if you'd picked a different combination you could have bought the self same Bosal tow-bar and paid two very different prices.
In your case, the car manufacturer should have exercised some diligence in making sure that the tow-bar they offer has the best corrosion and build qualities, but then again, if it's a dealer fit item - they may just get a local fitter to do the job - and then you could easily end up with a Towsure, EECO, or other tow-bar.
We've always bought detachable tow-bars that I know are used as OEM products from the manufacturers - Bosal, Brink or Westfalia - and have them fitted by a specialist independent fitter who I know is used by the local MB dealership.
Robert
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