In my opinion, a good compromise between DRM and just giving everyone an epub file is watermarking.
For me at least, watermarks do the job much better. I can consume the content in any way I choose, but I can't share it. DRM is usually breakable, and you can do whatever you wish with the content after you break it. With watermarks, however, you never know whether you've fully removed them or not, so you're actually afraid of sharing your content, even if you're technically able to do so.
The only problem with watermarking is that it doesn't really work with the streaming model, as not giving you access when the subscription expires is the whole point.
For me at least, watermarks do the job much better. I can consume the content in any way I choose, but I can't share it. DRM is usually breakable, and you can do whatever you wish with the content after you break it. With watermarks, however, you never know whether you've fully removed them or not, so you're actually afraid of sharing your content, even if you're technically able to do so.
The only problem with watermarking is that it doesn't really work with the streaming model, as not giving you access when the subscription expires is the whole point.