Differences & Similarities between I2C & SPI Analyzers
There is no functional difference between them. They're just logic analyzers that are optimized for one protocol or the other. They might have implementation differences such as header types, pin counts, or voltage/current tolerances, but those are just a result of the manufacturer targeting one protocol or another. They may also have firmware or client-side software that helps the user decipher protocol control signals and data, as opposed to a normal logic analyzer that just displays signals and timing diagrams.

In fact, you'll find many devices out there that can analyze both, such as the Beagle I2C/SPI Analyzer.

The similarities are too numerous to count because they're just different flavors of the same thing. The differences are superficial.