Low level is easy enough in small hops, which is what most pilots do.
Long flights across France are quite difficult to plan at low levels, due to the amount of low level restrictions to check out. It's true that most of it is inactive on any given day, particularly at weekends, but it still needs to be checked out, or in-flight diversions planned.
That said, the French (and just about everybody outside the UK) are much more casual about Class D transits than the UK where one has to sit up and beg and hope for the best (and have a diversion planned).