a single rocket launch (I assume they need to test their engines at altitude / hypersonic speed) would eat a lot of that.
Did no one tell you what happens when you "assume" things?
The pre cooler at the front of the engine decouples the air temperature (cryogenic) and velocity (about M0.5) from the ambient
environment (up to 1000c and M5.5)
Pre coolers with this power to weight ratio and ability to do frost control have never been done before, which is why this had to be tested first as a failure would have been game over for the whole project.
What that means is (unlike the SCramjets) you don't need to put it on a rocket to test its performance, although putting it on some kind of test vehicle would be a bonus.
Most of this can be found on the technical documents on the REL website.