The spoons are the weak point. They can't take side thrust without being damaged. I learned the hard way that once they're bent, you just can't bend them to straighten them. If they don't snap immediately they won't last long.
The idea of the spoon is to extract a plug of soil without compacting the soil. So if you're thinking about aerating to get oxygen into the soil, you need to avoid compaction. That means a solid rod is going to compact the soil and compromise the effort.