I doubt seriously that the Mossberg barrel is any more or less efficient than any other modern inline muzzle loader. The thing really is just a metal tube with rifling. How much can you expect it to change from one to the other?
It does seem to have a high rifle twist, making sabots a good bet for accurate shooting. 1 in 26 inches. Most traditional muskets are twice that, like 1 in 40 inches. The high twist is good if you use sabots, and ought to really get that bullet spinning good. Just remember to clean the barrel every single time you shoot and reload due to the plastic residue left behind from even just one sabot.
I am curious about them as well, but then again I would most likely buy myself a double barrel Kodiak Express from Pedersoli if I were to hunt deer with a musket. The second shot might be better for that. A Kodiak will be $850, so a Mossberg 500 barrel for only $103 per the Mossberg website is a better choice if you want to save money.
