With an IVA it explicitly says that GPS speedos are not permitted.
MOT criteria doesn't always align with IVA criteria though as I'm finding out whilst researching it all! To the extent where in theory, for some crtieria, you would pass the IVA and then fail your first MOT if you find yourself with a very strict tester.
So check what the MOT requires I reckon. As long as you've still got an odometer too as others have mentioned.