The (adjustable) length is almost the longest position (5 cm before the end of the adjustment) sufficient comfort to strap a Labi with 60 cm shoulder height on the chest harness. Crash Test I have not done and I like to live well. Because I think that the dog transport in the trunk (of course not in limousines!) And maybe even a pet carrier located there is still the safest solution for dog and owner / owner.
But as a "stopgap" the adapter is perfect - and inexpensive -.