My current gf is the first one to use anal beads on me and it was amazing. She first and foremost graciously lubed them up then slowly slid them in during oral. When she pulled them out during my orgasm it felt amazing. I agree with everyone about material, this is important so you don't get any weird infections that are difficult to explain later. Just remember cleanliness is next to godliness.
I also want to add, my gf had a random idea one time to put in the beads, then touch the beads with a vibrator during oral and that felt downright amazing, she also another time gave them a gentle tug which was also so exciting.