I don't have any internal attachments in TheBrain, but I have a ton of external attachments now. Everything lives in Dropbox or DEVONthink, so I link back to the files on either Dropbox or DEVONthink. With external attachments (meaning those that live in the Finder, not DEVONthink links) it uses Spotlight indexing to search, so you can search within TheBrain for text inside a document that externally attached.
At this point, I can't live without Thought Types and Tags. For example, in my types, I have Books and Movies, in Tags, I have To Read and To Watch, also Read and Watched. I created a report of all books that I marked to read, same for movies. Over the last eight months, I now have a real tracking system for what I watch and what I read with dates started and finished. I also do this for articles or papers for grad school.
There seems no concept of automated surfacing of links. It relies on the user having created effective links between items previously. Then the user can later 'see' these links. It would be nice to have a 'see also' element as per DEVONthink
It is expensive, especially given the US:AUD exchange rate currently. It virtually makes it a non-starter. US415 as at 2019-01-12.
It seems to peg my MacBook Pro’s CPU.