it’s good. since you can use sapper skills while holding a musket. So you don’t have to swap back and forth between bow and musket or smt like that. Sapper3 provide a good aoe skill (broom trap in circle3 got 50% crit chance) that musketeers lack of. Appraiser is bad for musketeer builds because only offhand weapon like dagger or pistol get the anvil bonus from overestimate skill.
Scout is a good option if you pvp alot. Flu Flu is a decent cc skill and flare is an okay filler skill.
But Rogue1 is a really nice filler. With lv5 sneak hit you get 40% crit chance with full werewolf card. And capture + broom trap is really good too. Try to get about 600+ crit rate with green gems and leather bonus and you’re good to go.
One more build that i’m using for my musketeer is A2-sap2-wugu2-musket2. You get more aoe skills with Gu Pot and 1v1 skill like needle blow, wugong gu help boost your damage alot in boss fights. Wugong gu + Broom trap + gu pot + covering fire blows every monster waves. I even can solo 16F with this build. The only downside is you don’t crit alot without rogue and broom trap c3 attribute.