I really like the express rifle sights on my shotgun.
One of the problems I've found with a bead sight is that, for me, the ability to hit consistently with a bead depends on a solid, consistent mount. This works out OK on trap and sporting clays fields, but becomes problematic in practical shooting matches or classes.
If I have a sloppy mount because I'm shooting on the move, from an unconventional position, or off the weakside shoulder or whatever, my ability to hit consistently is going to be compromised with a bead. With a set of sights, I can pick up a sight picture and make the hit, irrespective of the quality of my mount / stockweld.
The nice thing about express sights is that if I do have a good mount, I can ignore the wide, shallow "V" rear and just use the giant golfball front as a bead. On the other hand, if I can feel that the mount is off, I can slow down, pick up a sight picture, and make sure I don't drop my shot.
Can I do OK with a bead in a match or class? Sure. But I will be more
consistent under those conditions if I have the option of confirming my allignment with a sight picture.
It's easy to be accurate to at least 50 yards with a bead and slugs,
Absolutely. I was in a class once with a number of shotguns equipped with rifle sights, ghost rings, and even a EOTech or two. The fellow with the best 75 yard slug groups was running a bead-sighted 21" 870 that he used for deer hunting. Indian not Arrow. Now, if we had to print groups off the weakside shoulder around a baracade for time, would that change? Obviously, I don't know if he would have struggled with a bead -- but I know I would have.