Paris Pass Card - worth it?

[Sioned11]

DS and his GF are going to Paris shortly and want to invest in Paris Pass cards. I've read mixed reviews - some say (actually, they are on the PP website) that it's worth every penny - others, elsewhere, that it's a bit of a con.

As DS wants his Pass to be his Christmas present from us, I'm taking value for money seriously! They're staying in the centre so I don't know how much traveling around they will do but they'll want to visit museums and galleries.

Does anyone have any experience of a Paris Pass - the full card or the travel or museums only cards? Any thoughts/ideas for alternatives would be welcome!

Will he be wanting to visit enough places to make the pass value for money? I've never really looked at it before but I'm quite sure that most of those discounts are covered by the Visite travelcard alone. That plus a museum pass if planning to visit a lot of them might be better value.

When do they go? If staying mon-sun the Navigo card is usually the cheapest for travelling round on the Metro, or even just a carnet of 10, if they don't think they will use public transport much.

Also how old is DS/GF. France tends to do cheaper rates for under 25s. Sort of a midway between child and adult prices at attraction and for transport.

Would putting the equivalent amount on a pre-pay € credit card be an alternative?

Thank you so much, Akallabeth, for this comprehensive response. I'll look into all these alternatives. I don't think they'll travel beyond the centre so much that the full Pass is necessarily worth it. I'll look at the Navigo card - thanks.

They are both under 25 so that's worth thinking about, too.