the Class Action is proposed on an ‘open’ basis, that is, for...

the Class Action is proposed on an ‘open’ basis, that is, for all AVZ shareholders who acquired AVZ shares or an interest in AVZ shares leading up to May 2022 . The proposed class action will be conducted on an ‘open’ basis, so All shareholders will still be considered in the class action even though you may not have not signed up or expressed an interest with Omni Bridgeway.
To formally opt-out of the class action, Omni Bridgeway are advising you will need to complete a court-issued opt-out notice at the appropriate time.

How much will the class action cost and how long would it last?
Well The court case would have to be held in the equivalent of a Supreme Court and involve QC's for approximately 5 years before an outcome was received. Is there any hope of recovering any value from this process? Highly unlikely.
If AVZ in not successful in getting its ML liquidators would be called before this process would even commence. IMO The Class Action is another process to spook investors when we come back to trading.