It is less corrosive than any other BP substitute. It does have less smoke, but a lot of us consider that a downside. The fouling thing is true, although depending on what you are shooting, you may or may not benefit from swabbing between shots. For sure it is easier to manage than others.
As for the higher velocity I don't think you can really state that as a 100% true fact. If we are talking volume of powder, not weight, I've seen plenty of instances 777 matched or exceeded the velocity of BH209 bulk for bulk. I think it's kind of a weird argument for a muzzleloader though, as there's really no reason you can't just use more powder. This is compounded by the maybe too general rule of thumb that most modern inlines can handle 150gr of blackpowder, or 150gr volume of a blackpowder substitute such as 777. Blackhorn 209 is the outlier in that it is generally stated that only 120gr volume is safe in most rifles. Now if you compare 150gr volume of 777 vs 120gr volume of BH209, I'm betting the 777 is faster in all but the rarest instances. I will say that both 777 and BH209 are likely going to produce higher velocities than pyrodex or real blackpowder almost every time bulk for bulk.