These cards are a beautiful way to communicate with 'higher consciousness' (or angels, 'god', your higher self, your unconscious, however you view it). I have come to use them almost daily as an inspiring way to tap into 'inner wisdom' or guidance for both mundane and important situations, and they never fail to uplift and reassure - sometimes surprisingly. The artwork is evocative and perfectly suited to the message, and they are also a lovely introduction to well-known saints and 'higher realms'. There is (as the title suggests) a bias towards christianity, and the catholic faith in particular, so I'm not sure their claim to be 'non-denominational' is entirely founded, but there are just as many generally inspirational cards as saint cards, and the booklet that accompanies them offers interpretations that apply to any faith (as well as a short biography of the saint where applicable).
Personally I have no particular faith, but would class myself as 'spiritual' - and these work very well for me. For those wanting something equally uplifting and truly non-denominational, I would suggest Cheryl Richardson's Grace cards ([...] I use both sets in combination. The Saints and Angels cards are a lovely gift, whether for yourself or another.