Honestly, if it were me and I was going to be paying $30-40k just for custom plates alone, I would use the normal plates.
I've been looking into custom plates too and came across this paper which sort of gives an overview of sorts. There also seems to many different 'systems' out there and some are machine-cut, some are 3d printed. From what I gather from here some other benefits are: better control over vertical movement, no errors introduced by wonky condyles, the ability to place screws over areas of best-quality bone, no plate bending and less surgery time.
http://orthofacial.es/wp-content/uploads/2017/09/custom-machined-miniplates.pdfThere's alot in the article but this is where they mention that in large advancements custom plates alone cannot offer perfect stability.
"Achieving stability of the fragments that have undergone osteotomy and avoiding relapse are the next goals. The rigid fixation has shown its advantages over other osteosynthesis systems, being necessary when lowering movements of the maxilla are performed or in great maxillary advancements. The OPS considers such stability by fabricating the miniplates from highly rigid grade 5 titanium machined from a titanium block and fixating them to good quality bone on the anterior midfacial buttress. The custom miniplates are machined to perfectly fit to the surface of the midfacial bone with no need for molding, which would compromise their properties.
In theory, these advances should improve on conventional osteosynthesis systems. However, in light of our study’s results, it is evident that, by themselves, they are not enough to provide perfect stability, especially when operating near the limits of skeletal movement, such as in cases of great advancements for OSA. In these severe cases, it is highly likely that early adaptive changes occur, especially at the dentoalveolar level, prompted by the surgical intervention itself. Thus it is not surprising that morphologic changes occur between the time of surgery and the time of postoperative CT. Several factors can play an important role in the early postoperative period, and these will influence final outcomes. Examples include the bone quality, the stability of the achieved occlusion, neuromuscular adaptation or secondary elastic therapy, and temporomandibular joint stability. Improving our knowledge of these factors and their destabilizing effects might represent one of the greatest challenges in OGS"
They also had normal miniplates available as backup. Not sure if that's standard, but you'd hope so!
"During surgery, maxillomandibular occlusal splints and an osteosynthesis system with conventional miniplates were available, in case we were unable to use the custom OPS."