How do I determine if a SSIS transform is non-blocking, partially blocking, or fully blocking?
An operation which is blocking must wait until all rows have been seen and handled before it can start populating buffers.

An operations which is partially-blocking writes data onto new buffers, which only get handled by the next operation once each buffer (typically just under 10,000 rows) is populated.

An operation which is non-blocking can have the subsequent operation working on the same buffer, as each row is handled.

But many texts will refer to 'partially-blocking' as 'non-blocking', as the behaviour is much closer to 'non-blocking' than 'blocking'.

You should be able to tell what's going on by watching the data flow run, and seeing when the numbers are increasing at each point.