What exactly is meant by 24-month plans being cheaper? Do you have to pay it all upfront, and you're just showing the monthly costs of that alotted payment?

You do pay for it all upfornt, but paying for 24-months all at once will net you a big discount compared to paying for 24 months month-by-month:

Profi account paid month by month - $9.85 x 24 = $236.40
Profi paid for in 24-month period - $164.40

Paying for all 24 months at once saves you over $70 versus paying month by month. Yes you pay a larger sum, but it's only once every two years and works out to less in the long run.

Thanks Danimal for addressing it. I just can add that you have to prepay for 24 months if you chose biannual option and we have listed your monthly cost $164.40/24=$6.85