I would even be ok with paying for a month to find out
Only option is to buy yourself a "Premium" it seems, but from the homepage it looks like you can claim full refund - no questions asked, in case it doesnt show to be thing you looked for, after some testing period. (Better check it out with them - but this fits with my impression of the friendly Todoist policies IMHO)
Yes, Morten is correct. If within 30 days, you aren't happy we will refund the payment.