Read customer reviews of the WooCommerce Quantity Manager WordPress plugin by Barn2.
Rated 5 out of 5 stars based on 8 customer reviews.
The plugin does what it is advertised as. Also it has API support (thats why we choose it). And it works for 10k+ products without any problems. Plus support is very good. They even send required documents before the purchase. Best money we've spent on Wordpress.
Nice plugin. We found a bug and notified the team. They fixed the issue within few days. Good job!