you're right. Cancel's in H1 are very painful because all the in-progress transactions have to be torn down completely. New transactions have to set them all up

you're right. Cancel's in H1 are very painful because all the in-progress transactions have to be torn down completely. New transactions have to set them all up again. H2 let's you just send the server a short message that says "stop sending that stream" and you can go ahead and pipeline a new request right along with that cancel. This happens a lot more than you think as you browse through a collection of things and are just scanning them and clicking the next button - that's a really common use case h2 will handle much better.