In the words of Keeley Effects:

The Keeley Compressor is the most popular boutique compressor in the
world.With well over 50,000 compressors built in our shop we have an
expert understanding of compression, limiting, and sustain.We know
what it takes to make an instrument sound like its been professionally
recorded.We know how to make your guitar jump from the mix. We know
how to make it fun and easy to play.Keeley Compression is how.