google search:
Metal Build followed the 2007 release of a similar line of partly diecast action figures under Gundam Fix Figuration Metal Composite, which focuses on Universal Century mecha and is based on the designs and artwork of Hajime Katoki. In contrast, Metal Build has focused on other timelines than Universal Century.
Metal build has more accessories like you mentioned, and also tends to be more detailed. Chogokin is usually designed with animation accuracy in mind, while metal build is stylised. Chogokin uses ratchet joints (better for longevity) while metal build is strictly friction.
while some may favor MB more than chogokin, I think it’s wrong to say chogokin is the budget line. It’s a different design approach. Simpler and more anime accurate design will feel less detailed but it’s meant to be that way, not to say it’s lower quality.