Version 3a and 3b should be a big improvement over V2, it should it is able to create a larger verity of penis sizes and is also able to create flaccid penises. It also works much better with more diffucult poses and angles.

3b was trained for more steps and with a larger training set and seems to be a bit better overall.

The recommended strength is 0.45-0.9, a higher strength tends to work better for poses from behind.

The Model has been trained on Ares Mix: https://civitai.com/models/6931/ares-mix

I recommend using it with https://civitai.com/models/6931/ares-mix or https://civitai.com/models/14324/mars-mix two of the most underrated models IMO.

But it also works well with other realistic models.

It also works surprisingly well with anime and 2.5D models.

You can also combine it with the various Futanari models available on Civitai to get specific results like for example large flaccid: https://civitai.com/models/11824/futa-large-flaccid-penis

Look at the samples for prompts