Short answer is yes.
The trial is free, but the product isn't, at the end of the trial the charge for the product is applied. Not sure what you mean by the comment "and charges you full price" surely that would be the same as the price you see going into the pre-payment/auto renewal arrangement.
Personally, I wouldn't use this prepayment mandate for any product not just Avast. Then again I'm using Avast Free as it suits my needs.
You should just be able to download the Avast Premium Security without this and use it for 30 days without a license/subscription. You will get reminders during that period to purchase and you may well get offered a deal to purchase.
So the next year would be the same, towards the end of the year you will get reminders to renew your license/subscription and again you may well get offered a deal purchase.
