Has anyone ever heard of these liner systems
Bear Creek - I and others have definitely heard of forever flex. The warranty is good for sure. I'd be interested to have your installer indicate why he prefers that brand over Flex King. As capecoaler mentioned the customer service at Flex King vendor is very good. I asked them i.e. vendor, in fact what was difference and he said they are exactly the same liner in terms of materials. I would be interested to hear from an installer/professional as to why one may be better than the other.
out of interest, I asked a forever flex vendor if they ovalize pipes where necessary and they said they do not recommend it - in their opinion it interferes with the flow. By contrast I asked the same question to Flex King vendor and they said that this is not true at all and that ovalizing the liner is not a problem as long as you go one inch larger prior to ovalizing.
congrats on getting a stove - a lot of people were unfortunate to have to wait till next year. I also bought an extra ash pan direct from Hitzer yesterday for $19+shipping - this was a great tip from JafaDog and means emptying the ash pan can be a relaxed event and not a rush. They have these in stock currently.