I agree with you that it would be great to see tighter integration from invoices to inventory.
But in the meantime, that import should certainly not be taking anywhere near that long (3 hours for 10%). There must be something in their environment that's getting in the way. Grab a copy of the client's data and run the same import on your machine to compare the time. Most likely culprit is an Anti-Virus / firewall program. Try adding exclusions for Adagio folders, disabling or even uninstalling the AV products to see if there's a difference(sometimes uninstalling is the only solution for certain AVs).
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Ryan Brohman
Kitchener, ON