I couldn't recommend Robust Netsuite Integrator enough. We experienced several hurdles connecting Netsuite and Shopify prior to engaging with this app. However, the team behind Robut NetSuite Integrator exceeded our expectations. They are professional, well-knowledged, and very responsive. Since our integration, we have had customizations completed in order to fit our business processes and their team has been there to help every step of the way. Inventory updates, product information, and sales orders are synced instantly - have nothing to fault.
Very quick & easy to setup - Inventory updates happen fast & orders sync instantly - we've used on multiple stores now - recommend.