Catholic schools will tend to have 'practising Catholic', often 'child baptised before 6 months' as entrance criteria, so unless you tick those boxes, you may not gain admission even if you apply.
Are they better? Essentially, any school that imposes any form of selection or barrier to entry will tend to have slightly higher results than a school serving the same area / socio-economic mix which does not operate any form of selection.
This is because even 'non ability based' selection criteria such as faith (evidenced by e.g. church attendance) selects AGAINST chaotic families, poorly-housed families or those who move rapidly between a series of temporary housing solutions, Traveller families, refugee families, families in which parents are iliterate or have no spoken or written English, families wgho are poorly informed about ghow the school system works etc.
Thus, on average, the families of the children who DO get in are slightly more educated, slightly more organised, slightly more literate, slightly more stable - and that has an effect on final academic results.
Catholic schools do tend to have more PP and EAL families than other 'schools that have some form of selection', but even so they will tend to be 'better' because they operate a form of selection within the local socio-economic mix, not because they are better schools.