We have been using shipstation for over a year and love using it but here recently we just started checking or shipping rates on Shopify and have learned that UPS rates are extremely much lower than the cost of ship station. Additionally we've also learned that the priority shipping is almost a dollar or two dollars less than ship station. However first class packaging service is pretty comparable to ship station so not much of a difference there but when you're shipping priority and UPS Shopify is definitely the way to go.
However, there will be some featured missed.... The BIG ONE is end of day form. We have find a new way to generate but the cost savings is HUGE. I can't remember the plan we are on but it's the middle one, I think the $79 a month and that might be why we are getting lower rates.
Anyone using third party shipping apps should spot check your rates.