I'm just starting to put the wires through this stuff and IMO the bends are designed by idiots. It is not possible to put a fish tape through as there are shoulders in the bend mouldings, so it is necessary to undo the cover plates and persuade the tape to avoid the shoulder with a finger. The last lot of cast steel bends I used worked perfectly. Why can't people get a simple product right?
Incidentally, conduit wire insulation appears to have much thicker insulation now than 40 years ago. Is this always the case?