HPBN is really well written, chapter 4 helped me understand TLS enough to debug a high latency issue at a previous job. There was an issue where a particularly incomplete TLS frame received and no subsequent bits for it led to a server waiting 30 min for the rest of the bits to arrive. HPBN was a huge help. I haven’t finished reading it but I remember there’s part of it that goes over the trade offs of increasing vs decreasing TLS frame sizes which is a low level knob I now know exists because of HPBN. Not sure if I’ll ever use it but it’s fascinating.