Preview Custom Primitive Data In Material Editor

Needing to set default values other than 0 in PrimitiveCustomData in the Material View also.

There seems to be more limitation on the PerInstanceCustomData node, versus converting a parameter into using PrimitiveCustomData

Specifically getting Errors about invalid node in Pixel/null/domain. There are some comments about nodes that are incompatible with the PerInstanceCustomData node. Why are these limits not on the Parameter Custom Data workflow?