I had an Interlock roof put on several years ago and I am not sure I agree with the statement “more expensive, sure”. While it does cost more to put on the roof, I think the payback more than covers the extra price.
I am sitting in my attic office, a place that got cold even with heat this time of year, it is warm now. It stays cooler in the summer as well which saves on cooling costs.
The sales person told me that it would be the case but I really didn’t believe it. I would buy this roof again in a heartbeat.