A bare copper conductor would effectively bond these while an insulated bonding conductor will not. Though in this case it seems rather unlikely that an injury fault would occur, it is possible for unbonded sections of metal conduit to become energized. It also seems 'most likely' that an installation with PVC risers would use PVC bends (most people would 'assume' that from looking at it, and think that is an important issue for any installation). The the cost of 'rated' connectors and bends to make four transitions from ridgid to PVC as shown make it an unlikely choice. The preferred method would be to make custom bends from full sticks of PVC since most damage to conductors occurs near connectors adjacent to bends whether caused by grit mixed in glue drips, rocks, or burrs and dents in metal. Though the code requires a bonding conductor, it makes no issue regarding insulated or bare. For example: the place a bare bonding conductor would prevent the most 'Hazard to Electrician Faults' is probably metal flex drops that become disconnected and cut into a hot wire. This applies to poorly installed EMT as well, and who hasn't gone onto a job and found those? Here's my favorite though: I was doing an energy upgrade for a sprawling remodled commercial establishment and found a panel with a 22 amp 208VAC 'phantom' load. The circuit fed parking lot lights with photo-cells. My first 'clue' was a new 50 amp breaker feeding old #8 wire. The owner had pavers remove a string of old concrete bolsters that were initially roadway light bases, and pave over them. It happened to rain the day I was testing the parking lot lights and noticed an area two feet wide and ten feet long steaming. I pointed out the 'dry' spot to the owner. Upon digging the spot up we discovered backhoe damage, unbonded conduit, and buried connections. His response was 'how much has this been costing me?' A bare copper conductor would prevent the breaker from being reset in any of these cases. The code is not a design tool, it is an absolute minimum legal standard. Complying with this minimum is not necessarily good work practice.