I think Hadders means London style contactless where no special product is needed and you can just use an ordinary bank card.
For Paris you can load the Navigo on to your phone with no separate card needed if it has the right hardware, most later models Samsungs are fine (other makes may work... no personal experience), last year you couldn't use an iPhone but this may have been sorted.
You can also top up a physical navigo pass using your phone if it can read and write to the card, again depends on phone hardware, most later model phones are OK.
Both solutions mean you arrive with your onward travel sorted, avoiding the queues and general mayhem at places like Gare du Nord.
Thinking about the London situation:
A lot of cards have a minimum fee which is applied to even the smallest transaction.
To be honest as a foreign visitor I would rather just pay a simple daily charge, that I understood. I am not going to want to navigate the complexities of the current contactless system in London particularly if English isnt my first language. No it wouldn't stop me visiting, but it is part of the overall 'impression' that you get of a tourist destination.