If the current CU is otherwise satisfactory, other than being plastic, I would suggest that you get advice from someone who is sensible, and who you can trust (and who is not 'looking for work') before you have that done, because, as I've said, it might really be unnecessary.... I plan to get a CU in the future, but it will be in-between tenants to reduce any upheaval for them.
As you will hopefully understand from what I have been writing, I totally agree.I feel this has been unfairly tested and is just taking advantage, and feel the comments on this back this up and the currant installation is safe.
Kind Regards, John