Is this the replacement for the discontinued breville bbl605xl hemisphere control blender that atk said was coming this fall?

Yes, this is the latest mid priced blender "Highly" Recommended by America's Test Kitchens. This was updated in the July/August 2019 Cook's Illustrated magazine. They do, indeed, state that they like the new Fresh & Furious model better than the discontinued Hemisphere with its more powerful motor and new "smoothie" button.

How is it with frozen fruit?

I chose this blender for my son’s Christmas gift because he loves to make smoothies and uses frozen fruits and ice. He actually killed my vitamix blender making smoothies. This blender has stood up to almost daily heavy use without any problems and loves it. And with the wide bottom, it is so easy to wash. I wholeheartedly recommend it.

How is this to clean? Have a glass container blender w/ rubber gaskets; its impossible to keep mold out of the tiny grooves in gasket - I want better.

The container part is all one piece it does not come apart. I remove it from the base and I wash the whole thing by hand,you have to be careful of the blades. Also, when it needs cleaning i have put water in it and run the auto clean on the machine and the water will blend away any pieces of food,etc then just rinse it out in the sink and air dry. It says you can put the container in the dishwasher but i can't fit it into my dishwasher it is to tall. It also says not to wash in the dishwasher to often so as not to ruin the blades and container.

What are the decibels for this blender when in use making nut milks; ideally, what are comparison decibels for different blenders?

It peaks out at 114 decibels and averages 94 decibels. These db levels cause hearing loss. I contacted Breville and they said mine is working as advertised.