The CMS part numbers are the premium stuff, compared to the GS part numbers that are value oriented, or the cheap crap like a house brand item. Say like O’Reilly’s Master Pro cheap line vs their Precision premium line. The difference is in the details.
While I’ve seen many use the same stamping, the bushings and ball joints are very usually different. Just for instance the bushings may dry rot a lot quicker on the GS vs the CMS. Ball joints may wear more quickly as well. Usually the cheaper stuff may last about 2 years compared to the more expensive ones lasting 4 years or more.
Sometimes you’ll get lucky. But in my years of experience, the cheap stuff does not hold up. You will likely be doing the job again and again with cheaper line parts. Not a problem if you’re just going to get rid of the car. But if you plan to keep it and want it reliable, don’t cheap out. The cheap ones are ok though. If installed correctly, they may last far beyond their intended use.
The biggest problem I see is when people tighten bolts on the bushings with the suspension off the ground. The bushings then will likely be under tension and tear. Also, not greasing the ball joint initially when installed. Most people thing they have enough grease out of the box. Sometimes they do, more times they don’t. So I always pump them full of grease. Usually tell the customer they need to re-grease about every 15,000 miles. That usually works the best.