Broadly speaking, this product makes no sense. If interest rates go up, the value of the loan goes down. If interest rates go down, the value of the loan goes up ... until the borrower unilaterally refinances and pays of the loan at face value.
Indeed, no bank actually holds fixed rate loans. Instead they immediately sell it to Fannie May/Freddie Mac, which were created by the government specifically to allow for a product as absurd as the 30 year fixed rate mortgage to exist.
The real winners are those who own before the government enforces new price inflation policies on the market. (The only reason we have 30 year fixed mortgages is because of government intervention in the market.)
From my US perspective, I would rather rent forever than risk such a loan, so I suppose there must be something else at play which makes your approach less awful than it would be if we did that here.
Also adjustable rates have been amazingly cheap in past and still are not that expensive. Like sub 1% total. And my adjustable rate loan would be 4.425% if it adjusted today.