Regarding machined perches and the issues that can result from their use are as follows:
The major problem is both the size (commonly undersized) and the lack of variation over its length! The sad reality is that far too many Parrots are left in undersized cages on undersized dowels for weeks, months, years! The results are the physical failure of their pads. The results is extensive pain as the open wound becomes infected, etc, etc...
I am well aware of the number of individuals that commonly use machine created perches i.e. dowels. And, I am equally aware of the length of time without problem. Point being, when properly sized natural perches are used, the Parrot's pads are faced with different loading as they move around on a nature perch. This provides a healthy, natural exercise of the pads (duplicating natural). Why not provide that small comfort to our Parrots!
FYI: Oval machined dowels, long term have the same effect if they become the standard replacement. The proper way to use an oval dowel is that the Parrot perches on the widest surfaces.