Check what you can actually play, what requires an account, and whether payment is needed to continue. “Free” is most useful when the site explains those boundaries before you begin.
Check the first playable step
A page of instructions is not the same as a playable game. Look for an action that opens the activity and lets you make a choice. Then check whether you can see its result without buying something.
Intuisity states that its guest games are free with no game limit. An email is not required for guest play; a free account adds personal features including Progress Reports.
Choose the amount of commitment you want
If you only want to try a game, begin as a guest. If you later want the account features, read the signup information and decide whether they are useful to you.
Keep account registration separate from permission for marketing messages. Read what the form says rather than assuming every email field has the same purpose.
You do not have to commit to a routine before the first round. Try an activity, see whether you like the choices and feedback, and make the next decision from experience.