author here: please note that this is what we did in 2016-2017 where kops(what we use to provision) did not support spot fleet yet.

also, this works out so well for our use case because we were using .net framework at the time so the cost saving was huge.

a lot has changes since then.

Also, this strategy is not limited to AWS, the similiar type of instances are also available on Azure, GCP, etc...