Sonor products are premium price but quite frankly I would go with 600 series (or basic arm system) over 4000 or 2000 any day. It's not that the metal is any different , it's the details and the features available on this high-end hardware series.
This particular cymbal arm is great (at least for me) because it offers so much versatility and flexibility with positioning cymbal holders (or percussion holders) anywhere on the rod (apart from where it is attached to the stand). The 4000 and 2000 just have fixed cymbal end - which makes it a bit limited and single purpose. This BA12L maybe 2-3 times the price of cheaper Sonor lines but has so many options. For example, it helps to keep the drum kit footprint smaller. I can fit a 20" ride and 18" crash on just one of these, one cymbal on each end of the bar. I keep both cymbals at a similar height and it just fits making my kit's footprint just one cymbal stand (tripod) instead of two on my right side.
