The games and pages on that list have some nice features. They help you practice and memorize useful "math facts" (addition, subtraction, multiplication, or division of two numbers), and give you practice at recalling them. Many people find them fun. Some of the pages give lots of information and explanations that can help you remember or learn math topics.
Some possible disadvantages to these games are that they:
- often emphasize speed and scoring, which can be stressful for some people and aren't all that related to math understanding
- generally don't lead to deep thinking about math concepts (the games on my Math Websites with Creative or Complicated Games list tend to be better for this)
- usually do not connect different math ideas; the problems are narrowly focused on certain skills
- hardly ever require complicated problem solving strategies
- may not meet middle school Common Core standards
- often do not involve "real world" problems or make you curious