We're using Fetch to deliver audio loop product files that are pretty large. Some of the files are over 500 GB. The reliability with Fetch is very good. Simple nice interface. Nice set of features. Easy to set up.
The customer user experience between Shopify and Fetch isn't as clean as I'd like for my customers. For example, Shopify isn't designed for digital downloads so customers are forced to provide a shipping address even though we're not shipping a product. There's a couple of klugy things like that. Over time, Shopify will likely clean those things up.
We have some free audio loop downloads on our site if you'd like to run through the order/download process to see if it suits your needs.