Rifled shotgun barrels are capable of very good accuracy.
A neighbor set up a Browning Gold Hunter for slug shooting in a shotgun only area. When he was done, he could hit a 5 gal bucket at 275 yds 10/10 times. Grouping was respectable, as well.
But, it was very picky with loads, only one sabot load would do this, others or rifled slugs would not group well, and he tried 8 different loads from various manufacturers.
Having the scope mount on the barrel, as in the article, makes a huge difference beyond 100 yds.
Are they effective against blue Kevlar?
Shotguns are amazingly versatile.