I presume you have to reinstall cats for the MOT, how long does that take and do you borrow them or have a used/cheap pair ? I don't have any facilities for doing it myself so would be concerned about the annual cost.
Its not a difficult job to change them just time consuming, I did mine with of axial stands.I have not got the the MOT time yet, I may just buy a second hand unit if I can find one just for the MOT.