Question: Which bundle type should I use for selling non-physical products?
Answer: Multiple SKU bundles.
This is because non-physical products function by sending the customer a download link upon purchasing.
As single SKU bundles use line item properties instead of SKUs for each individual product, Shopify's platform does not have enough information to send download links. Multiple SKU bundles do not face this issue, and will therefore send your customers the correct downloads.