I noticed once that in the wordpress importer you were able to make a choice which posts you would like to import, say only the posts of December. Tumblr importer doesn’t seem to have that feature.
You’re correct. The importer here is more of a migration tool, for people looking to move off Tumblr to a more capable self-hosted WordPress blog.
Secondly I noticed that all imports are published immediately whereas with the Press This snippet you can make the choice of saving the clipping in draft or saving and publishing it immediately.
This is because the tool supports importing of Drafts from Tumblr as well. So if you have a draft post in tumblr, then it will be a draft on import and not published. If it offered this option, then you wouldn’t be able to sort out the drafts from the published posts.
Also, again, this is a migration tool. It’s presumed that you’re moving from one blog to another. If you want partial imports or to pick and choose your posts, this isn’t necessarily the tool you want to use. At least, not yet. It’s a work in progress, basically.