mRNA therapies have been studied for years in other interventions. It's also a naturally occurring substance that's contained in every cell of the body, so it's hardly a "completely novel technology"
mRNA is a naturally occurring substance.
Inducing mRNA to produce proteins is a relatively new technology.
Inducing mRNA to produce proteins in response to a vaccine is totally new (has been tried before, but not successfully).
No one knows whether the immune response produced actually induces the same immunity as a normal vaccine.
Even with conventional vaccine technology, many potential vaccines which produce an immune response turn out to have no real-world effect.
The initial trial data from Pfizer and Moderna is hopeful, but it's early days. It may turn out to be more spin than substance, or it may turn out that the vaccines are effective, but only in certain scenarios.
I suspect we will see a tortoise and hare scenario, with AZ as the tortoise that turns out to be the winner. I don't have shares in any pharma company but if I did, I'd be buying more AZ! (And, no, I don't work for them or have any affliliation to them)