I know this is an old question, but I have tried both Mortgage Watchdog and Interest savers and find them both good. However to get value you need to buy them. Don't cheap out they are worth it. The first time I checked my loan statements I was only being over charged .06c. Big deal I thought! Well next time I checked I was being stung $968! The reason? A change in interest rate was not actioned. After many letters and stat dec's the bank refunded the overcharge. The mortgage checker was an integral part of the proof process. Which ever you get, it is worth it and tax deductible if you are a property investor. 

Jeremy
http://www.loansense.com.au