Used as a 'mantra' prayer, the repetition involved in a rosary makes sense. As for the 'prayer-bead' part,we should be thankful for that muslim contribution - a practice the 'crusaders' picked up during the crusader times. 

Before that, some saints  promoted the repetition of the Gospel passages 'hail, Mary - full of grace. The Lord is with thee; blessed are you among women and blessed is the fruit of your womb': Jesus. The second portion was gradually added over time.

 St. Dominic's version of a 5 decade prayer bead and meditating on the Joyful, Sorrowful, and Glorious mysterious of the life of Jesus became most popular, other forms were also used
.
The Franciscans favored a seven decade rosary, meditating on Joyful 'mysteries' of Jesus' life.

The only 'caution' I would recommend is about when somebody has 'visions' attaching all sorts of 'promises' to the prayer. Those are often rather dubious,  to my mind at least. The  rosary as mantra prayer should stand on its own merits.