I've used these stacking corners on four custom-built bass cabinets, and overall they work very well. They stack nicely and give the cabs a clean, professional look. Installation is easy, but you have to be careful not to overtighten the screws — the plastic will bend if you're not careful.
One downside is durability. The plastic isn't super tough, and I had one corner crack during loading into a car. That said, it's only happened once, and they’ve held up fine otherwise.
Important tip: Your cabinet needs to have rounded edges for a perfect fit. I used a handheld router, which made the job much easier.
Great for DIY cabs, but not the most rugged choice if your gear takes a lot of abuse.