Sanity has a personalization plugin already, why add a separate tool?

The honest gap is that the Sanity plugin models variants in Studio but does not assign traffic or measure results. It gives you the content structure for variants, and then leaves the two hard parts to you: deciding which visitor sees which variant, and working out whether it won.

So you end up writing the bucketing yourself and wiring up some external analytics to read the outcome. That is the part a dedicated tool covers. Croct adds real-time audience assignment evaluated per interaction, plus a built-in Bayesian, unsampled analytics engine, with no external CDP in the loop. If you are happy building assignment and stats yourself, the plugin alone is fine. Most teams find that is where the effort actually is.