Question about trigram GIST index

So, for my use case I simply need to search for a case insensitive
substring. It need not be super exact. It seems like there are two ways I
can do this:

CREATE INDEX idx_users_name ON users USING GIST(lower(name) gist_trgm_ops);
SELECT * FROM users WHERE lower(name) LIKE '%john%';

Or I can do it like this:

CREATE INDEX idx_users_name ON users USING GIST(name gist_trgm_ops);
SELECT * FROM users WHERE name % 'john';

Unfortunately I cannot find any documentation on the trade-offs between
these two approaches. For my test dataset of 75K records the query speed
seems pretty damn similar.

So, I guess my question is, what is the difference for querying and insert
for the two approaches?

Thanks!