To add to this, it's essentially a case of "we don't now how the law would handle it, if police were alerted to you using one, or if you were stopped with one by police". The police will likely believe that it is prohibited, because the FRT tells them it is. Your lawyer, if you were charged, would say that it's not prohibited. The judge of the eventual court case (if it goes that far) would then determine if you were legally using it at the time that police stopped you. This would help resolve some of the concerns about it's legal status for everyone else, but it would be expensive for you to find out. If it were to go poorly for you on specifically the question of "is it prohibited", then it could impact the community negatively. If you were to win that question, then it would likely help ATRS' case against the RCMP.
The litigation that ATRS is pursuing is to argue that despite the RCMP's belief that the MS series are prohibited by the OIC, the MS series are not in fact captured by the OIC because they are not a variant of the AR15 or AR10. This is how the RCMP felt previously to the OIC, and then the FRT was edited to consider the MS series a variant of a banned platform.
The decision in this case will have serious knock-on effects as far as the legality of classifications determined by the RCMP and logged in the FRT.