Amazon MCF by ByteStand

ByteStand works really well for our setup.
It automatically sends our Germany and UK orders to Amazon for MCF fulfillment, including subscription and upsell orders, which saves a lot of manual work. The Virtual Bundle feature also makes it easy to map product bundles.
Inventory syncing is smooth too - FBA quantities are updated in Shopify automatically.
Simple, reliable, and does what it’s supposed to.