From the cherry-picked example-images on that page, it seems like Imagen more closely follows the prompt than the open Stable Diffusion model[0]. Stable Diffusion needs a lot of hints before it makes out of the ordinary pictures.

In general, I think these models are a great and funny toy, but not a threat to stock-photos yet. This may change within a year or three years though.

[0]:https://stability.ai/blog/stable-diffusion-announcement