Ultimately you still do not own these books, just like with Amazon, because they are locked into a DRM and proprietary reader, so your "purchase" can be rescinded or orphaned at any time...
• Ebooks from Bookshop.org must be read on either our Apple or Android app, or via a web browser. • Users of Android based e ink devices, that have regular access to the Google Play app store (Boox, Meebook, etc), should be able to download and read from our Android app. • Due to Amazon's and Barnes & Noble’s proprietary digital rights management software (DRM) and publishers' DRM requirements, it’s not currently possible to buy ebooks from Bookshop.org or local bookstores and read them on your Kindle or Nook.
Fixed that for you...