Yes, it is and you'll be charged once a month. But there are absolutely no contracts and you can cancel at anytime.
You can unlock a new PRO course every 30 days on the Value plan. On the Unlimited plan, you can enroll all courses anytime you want.
You have access to courses that you enrolled as long as you're subscribed or your subscription date is not expired yet.
You can cancel your subscription anytime and re-subscribe again later on. Once you re-subscribed, you can keep going with courses that you already subscribed before.