I must admit that at first I too thought that the new window laws would permanently mandate a 12.5 mm opening. I am very pleased that this is not the case.
Perhaps the window installers that you have approached also had the same interpretation and have bulk bought these permanent locks which they are now trying to off load on to schemes that are not so knowledgeable.
Would it be worth your scheme buying good quality locks that suit your purpose and then pay a certified trades person to install the locks that your scheme has purchased? Or you could just keep on looking for a company that has actually understood the ramifications of the new laws.