The best players in the world and pros at Las Vegas always kept notes. Stu Ungar could do it in his head but that's a bit difficult for mere mortals. Keeping notes in your textbook or google notepad is cumbersome. You can't search for someone easily and you can't go back and forth those who are currently at your table. AceNotes gives you the ability to keep notes like you do with a HUD online.
This is not something recreational players need. But if you care about your winrate and you play often, not matter which stakes you play the price is maybe 1-10 BB per month. If the app makes you 1BB per *hour* more profitable we would say it's a super valuable investment. Especially when someone with something distinctive comes to your table and you can see from your notes that he is a huge maniacal bluffer. That fold that turns into a profitable call will pay for all the yearly subscription.
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