That pipe will remove the front downpipe cat. It will offer better exhaust flow across the rpm range. As others have stated, it is fine for MOT. Removal of the stock pipe might prove to be a little bit of a pain for you as the cat limits the space with which to work. Fitting a replacement such as the one in the link is much easier as more space to work in bolting it onto the turbine housing.
Upside is now you know how to do the filter