Hi, 

For the most part, it is a personal preference. Labels on concrete products don't often list all the ingredients used, or if they are dyed, what was in the dye. You could use a sealer on the interior as an option. The making of concrete uses fly ash in the process which can contain heavy metals. 

The other consideration is that they will retain heat more than wood. This could cause the soil around the outer edge to warm up faster in the spring and dry out faster in the summer for watering purposes.

Perhaps a dry-stacked natural stone bed would an option if you wanted a stone material. You could weigh the costs between the two.

There are many metal-type raised beds available now too.

Emily