I have a GD 24 Heures in Periwinkle Blue. I find it a fantastic bag. Mine is calf leather, very soft and strong. I've had it for over a year now and it looks even better than the day I bought it. It fits easily on my shoulder and I can find everything in it. In any case, a pouch or purse organizer can be slipped inside. In the basic version there's no mobile phone pocket, but that doesn't bother me. I know some people say this bag splays 'like an amoeba' when you set it down. I don't find this a probem. My Balenciaga Twiggy is now very soft and behaves in a similar way.
And yes, they are still very popular in France. Whenever I go there I see lots of them, especially the 24 Heures. I have seen quite a few of them on eBay, and they seem to sell for about £200 or so. It's not an exorbitantly expensive bag, even when bought new. Best to ask about the leather quality first though. I've heard that earlier batches weren't so good. Mine has a very slight sheen to the leather and still has the leather smell. I bought mine new, but I'd say a good, used one could be perfect for your needs. I love my GD! Good luck with your hunting/purchasing!