Based on the comment on max below that's not read-after-write consistency but it just becomes eventually consistent but ideally within ~150ms. What would be the consequences of bypassing the cache for read after write, does that break your model in any way? (I guess at the very least you will lose your statistics feature)
You can bypass the cache if you want to, but it's not necessary. As it would just be like a Cache MISS, that would totally work.
We have a limit - you can only "tag" up to 1k items within one query. If you have more items in there, we can't purge all of them.
Due to the nature of the broadcast protocol of Fastlys purging implementation, I assume that it scales quite well - they have really big customers using this for a few years already.
We're using Fastly ourselves and I was not aware up until today (and in fact I'm taking your word for it, since I can't find it in the docs) that fastly provides consistency guarantees for purges.