Starsweeper XXIs are the brooms ridden by the United States National Team during the Quidditch World Cup tournament of 2014 (Pm).
We don't know much about this broom. XXI may stand for "twenty-first century" or there may have been twenty previous models. If the latter, they are likely to have been manufactured to meet demand for the North American broom game of Quodpot.
Lexicon list of Broom Manufacturers
From the Web
Writing by J.K. Rowling on Pottermore:
- History of the Quidditch World Cup
- 2014 Quidditch World Cup reports
- 2014 Quidditch World Cup final
- The Daily Prophet
Pottermore enhanced reading experience: Quidditch World Cup
Screenshots of the original Daily Prophet coverage of the 2014 Quidditch World Cup on Pottermore: Imgur archive
Harry Potter Wiki: Brooms
Tags: competitions/competitors fast racing brooms skills speed