Quote History Slidefire bought the property rights for their improvements and they patented some other improvement together iirc. No idea who did the actual manufacturing, but there are some differences between the 2 models, I assume improvements to make machining them easier. The VA version is not interchangeable with the Slidefire version, there's a difference externally where they sit in the lower receiver.
I'm assuming the ejection chute not requiring the fin and the notched links was the collaborative patent , which is a huge improvement because notching the links sucks. Standard 249 links, if you get most of them off the ground at the end of shooting its okay. With the notched links, you're counting every one to make sure you get them all picked up and looking around some more just in case.