Ah that was only about the review on how the new model images look compared to the old ones. You can run it locally too.
Dreamstudio is legit, it's owned by the company that made stablediffusion. Until they released sdxl I think people could only test the new model on their site, to preview beta versions.
Most people won't use the actual sdxl model but new models (checkpoints) trained by others, like
https://civitai.com/tag/sdxl. It's the same now, all the fancy images you see around are not made with the actualy stablediffusion-v1.5 model, but with other custom models that look way better. Entirely so for nsfw images.
At the moment SD1.5 custom models still look better or just about the same in many ways compared to SDXL, and are considerably quicker. So it remains to be seen when (or if) new custom models will be made to push SDXL to its potential and make it worth the performance cost, or if it will suffer the same fate as SD2