My dad ran a concrete business for many years, so my one 'new' contribution to this thread is: over time, concrete gradually leaches lime to the soil. If your soil is acidic, this may be a plus. If you have alkaline soil, it will add a slight impact to the alkalinity.
Having said that, I used raised concrete block beds once upon a time... if you stack higher, stagger the tiers so the blocks on the row above overlaps the blocks below by half.... the upper block should cover half (the ends) of two blocks below. It's more stable.
And if you do decide to paint, use a paint intended for concrete, it will last for years. Unlike metal, BTW, concrete does not get hot in summer sun... nor rot, as untreated wood will eventually do. (I never use treated wood, I don't want the toxic chemicals in my yard ... or where I 'may' plant food.) I did plant creeping phlox into the holes in the concrete, it worked spectacularly.
One last note: if your raised beds are below the eaves of the house, set them so the rain goes 'into' the raised bed, not onto the edges with the holes. The rain from the eaves will splash into the holes and, over time, wash the dirt out and damage or kill plants in the holes. Bring the bed out a bit further, so the rain drips into the bed (and a hard rain, which may be damaging, will overshoot the bed).
If the beds are not near the house, then no worries. They hold up for a very long time. The dirt may settle, so you will find yourself topping them off from time to time, but otherwise they work very well. Sorry I don't have pictures to put up, but they are not digital (back in the day).
