Ahhh that's great thank you
![Emoticon Smile Emoticon Smile](/media/com_easydiscuss/images/markitup/emoticon-smile.png)
I was doing it completely the wrong way, thinking the ordinary categories module would allow selection!
For those also doing this, go to modules, make a new module, and like Indresh says, set it to be ordinary category, but then filter for a product category you want.
Then in SP Page Builder, add a row, add in Joomla module block, and select the name of the module you just made
![Emoticon Smile Emoticon Smile](/media/com_easydiscuss/images/markitup/emoticon-smile.png)
Beware the name you gave the module just above filter will also appear so no need to give title.