The 'Leylandii' will literally smother the Photinia 'Red Robin' over time ! These conifers are erroneously still planted by many garden owners ; much to their regret later on . Best avoided .
'Red Robin' is an attractive shrub in its own right . Pruning can be tricky as dieback may well occur if too drastic (i.e squarely cut) . If planted and then left to develop naturally , but keeping straggly growth under control , I can't forsee any major problems .
There is available another Photinia, called ( Stranvaesia) davidiana 'Palette' ; this is an attractive variegated form bearing red berries , cream,green and red leaves and good Autumn colouration too .
Could form an interesting association as a hedge .
PS :- Both forms appreciate a good fertile loamy soil , maybe even slightly acidic and moist for optimum growth