I found it worked quite well. Mixed mine with a small amount of water so it would fill the entire lower half of my bong. I then nuked the mixture before pouring it in so it was hot.
Let it sit for an hour then poured in some dry rice and sloshed it around. Nearly all the tar was gone.
Its a cleaner for regular use so if you have a very tar filled bong get a couple of bottles and use it neat. Make sure you heat em first though. Tar is a lot easier to move once its hot.