After a 20+ career in Purchasing, I now do business and marketing consulting. I am currently developing a WordPress website for a client, using WooCommerce, linked to his eBay account. It's all working well. We are implementing ATUM on his site. It is a good product, and I know you are making constant improvements.
Here are a couple of suggestions for the PO section. Stock Central is a very good feature, but it would be WAY BETTER and WAY more useful if you could, first, filter by supplier, then from the results, review each item, tag each item for order, AND, include a quantity to order, when done, with one button, create the PO.
Next, from the PO screen, I am not seeing a way to directly e-mail or fax of the PO to the supplier. Is that possible now, or is it a paid version upgrade?
Finally, there needs to be a way to order the same item from multiple suppliers. That is a real world scenario in the Purchasing world. Products need to be "tagged" for potential/possible purchase from multiple suppliers, and then when it is ordered from one supplier, it pulls over their last purchase cost.
Beyond this, I would say you are working on a GREAT product.
As an ex-Purchasing and Inventory Control professional, I would be happy to consult with you on your product, at no charge from me, but let me implement your paid products and updates with my client at no charge as well.
My target market(s) definitely have a need for your product(s).