Not all metal plates are created equal.
For the most part, metal plates are not there to look pretty, they are there to add more weight to the bar when you run out of bumpers or run out of room for bumpers. They are also the only way to get to precise weights so you can go up in increments smaller than 20 pounds at a time. Most metal plates will get the job done. However, many of the plates available at local sporting goods stores are particularly low quality. Generally this does not cause problems, since they are designed to be used for slow lifts, and for the most part are used solely for bench press by their intended audience. When CrossFitters, buy these cast iron plates, they will work well for a while. After all, they are using them with bumper plates that are taking the impact of the drops. However, particularly with the 2.5 and 5 pound plates, those repeated sudden stops can be enough to cause the plates to break.
The Ader Black Plates, being made from higher quality cast iron, and are much less likely to break due to impact when dropped with bumpers.
Since they are available in weights as low as 1.25 pounds, they are also an inexpensive way to go up 2.5 pounds at a time for lifts like shoulder press, where often 5 pounds can be the difference between an easy lift and an impossible one.