I forgot to say that if the towbar is OK for the AlKo it will also be OK for the Winterhoff.
In addition to having to comply with the standard towball dimensions specified in Annex V paragraph 1.4 of EU Directive 94/20/EC, the above stabilisers require at least 85mm of unrestricted movement, measured from the centre of the towball. (The EU standard only requires 65mm to the bumper and, in the case of bolt-on brackets, 40mm to the mounting flange.) That's why brackets for use with these stabilisers are specific. Swan neck towbars, of course, don't have a flange which could get in the way. Both stabilisers also require undercuts under the towball but these are specified in the standard.