Cape' thanks for info below
I just called the above vendor to ask about the specifics of this adaptor. I asked :
1. how do you create a good seal with stove he said using cement/high temp sealant. I asked if this would be air tight and he confirmed yes.
2. Then I asked on the top i.e. where the liner is inserted into the adaptor, how is that sealed and he confirmed, as would be expected, using the hose ring supplied. I asked if this is an air tight seal and he said "no nor does it have to be that the chimney will suck anything right up" i.e. it's not going to leak there. also this adaptor he confirmed comes with their kits
Very helpful and nice people to deal with. Am so accustomed to rude and unhelpful people in NYC that calling around the country as I have been doing is like a vacation back to Ireland where I am from.