This mod will end up costing you more in shipping than it could possible save you in time. You cannot select what level of shipping you want to use nor can you adjust the weight. I will explain:
1. There are several different levels of priority mail mostly determined by the size of the package like Small Flat Rate, Medium Flat Rate, Large Flat Rate, Flat Rate Envelope...This addon will only allow you to use parcel which will totally throw off the cost of the label.
2. It only takes into account the weight of the product and and doesn't allow you to adjust the weight unless you go in each time you create a shipment and adjust the weight of the items in the order. So it does not account for the box itself if it is your own box or the weight a packing material and any promotional materials you add to the package. This would cost allot of money in adjustment fees from Endicia. This would be more time consuming than creating labels manually.
I have pointed this out to Webkul and they agree this is the way it works.
