Without spending too much time on it the points were:

Ketosis can shrink kidney stones. If you have a big unpassable kidney stone it's relatively harmless. If it shrinks it can get stuck in a place that causes excruciating pain.

Ketosis can cause heart rhythm irregularities if you have certain heart conditions. Maybe just temporarily.

Ketosis may cause fasting hyperglycemia (high blood sugar) in some people.

Ketosis may cause cramping in some people. Sometimes taking minerals helps.

The author then goes on to say he doesn't worry about it, he drifts in and out of ketosis all the time (we all do every night anyway).

The biggest difference is low carbers tend to make it a 24 hour a day thing versus something you're doing a few hours a night.