1. Who fills in the record. This is the criterion that decides whether the tool survives month three. There are three answers in this category: you type it (Monica, Notion, a spreadsheet), the tool syncs a capped slice of LinkedIn and your inbox (Dex, Mesh, folk), or it reads your full inbox and calendar history and builds the graph from what already happened (Happenstance, Cloze). Records you maintain by hand go stale. Everything else is a question of how much gets covered.
2. Whether the free plan is a plan or a countdown. Three of the seven have no free plan at all, only trials of seven to fourteen days, and Monica's free option means running the server yourself. Mesh and Contacts+ publish real free tiers with stated caps. Read the cap, not the word free.
3. Reminders and notes. The core of the category. If being nudged is the reason you're shopping, weight this above everything else: Dex, Mesh, Monica and Contacts+ have it, and Happenstance and Covve are built for other jobs.
4. What you can ask it. Almost every tool here gives you filters over a list you built. Very few will answer a question you haven't pre-tagged for, like which of the people I know have worked at a payments company.
5. Getting the data back out. A personal CRM holds a decade of context about people you like. Check for export before you import. Monica publishes data export on its plan page, Contacts+ backs up the accounts it syncs, and Happenstance exports search results to CSV on Pro.