That’s a common question and a good one, so well done on some critical thinking. There’s not enough of that in this crazy world anymore. But back to your question…
The short answer is there is no difference between French and Jumbo guinea fowl. There are different bloodlines since a hatchery may breed and maintain their own strain of fowl (although in reality most hatcheries in America purchase their eggs from the same imported breeder flock) but basically the characteristics between French guinea fowl and Jumbo guinea fowl are the same. In fact, the term “French” and “Jumbo” are used interchangeably.
Although guinea fowl originated in Africa, the French have been breeding poultry for centuries and have developed a strain of guinea fowl from selectively breeding larger fowl throughout the generations. This is because the French have used guinea fowl for meat production and so they had good reason to want a heavier guinea producing more meat. Guinea fowl have lean dark meat similar to a pheasant. This market demand has resulted in a naturally selected bigger strain of guinea fowl known as the “French Guinea.” It’s a completely natural guinea in every way except it reaches a larger size (up to 2 lbs heavier) in a shorter time than the common guinea fowl. The French guinea retains all the natural instincts of the common fowl such as foraging and eating ticks, watchdog personalities, and strong relationships with other fowl.
Some folks say that Jumbo guinea fowl need to be artificially inseminated. Hatcheries do need to use artificial insemination but not because the French guinea is incapable of reproduction due to it’s size. That’s fake news! The real reason is that guinea fowl have a short breeding season in the spring and guinea fowl are monogamous so if only natural reproduction was used, guinea fowl would only be available for a short time of the year and they would cost a lot more because natural breeding is slow and difficult in captivity. Artificial insemination allows hatcheries to hatch guineas affordably and reliably. French guinea fowl are perfectly capable of natural reproduction. However, it must be noted that any guinea fowl strain will not reproduce well in captivity.
Another rumor is that French guinea’s are too heavy to fly. This is not true. If your flock is kept on a limited diet through summer, they will fly well but still prefer to run.