Another question, the customer is telling me that they want to use ShipStation instead of Netsuite WMS I have no opinion. What do you think ?

Not entirely sure about ShipStation but ShipHawk / RF-Smart shipping are good alternatives.

My environment uses ShipRush (a Descartes / Oz Development product) and it gave us a lot more visibility both at the shipping station (to rate shop easily) as well as our final rated cost getting written back to NetSuite for shipping profitability analysis. I've used ShipStation -- but not with NetSuite. It seemed like a decent third part app. If the integration is anything like ShipRush, it'll probably work great. I have colleagues that used RF Smart and like it as well. Lots of options that work better than the "built in" shipping functionalities.

Do give it a try for RF smart It's much better compared to other solutions. Or shipHawk.

I recommend Pacejet for any shipping needs

ShipStation has limitations, so it depends on your requirements. ShipHawk is a really nice solution. I've used PaceJet, it can work too, but I ultimately replaced it with a custom solution for the one client that used it.