Great resource I've been using Vitalsource since I discovered it in 2019. I was tired of carrying around textbooks and at the time most eBooks were still on Adobe's Digital Editions software, which was a very barebones reader more concerned with DRM protection than offering an actual reading experience, to put it nicely. When I mention Vitalsource, I'm referring to two things: 1. The eBook store, and 2. the Bookshelf app that they author. The Store --Selection The VitalSource store has a good selection of textbooks. Most books you'd need for school (or supplemental learning) on mathematics, physics, and computer science authored within the last 10 years are there. --Purchases and Refunds Purchases and access are easy. Most books have both rental and lifetime purchase options. The options seem to be dictated by the publisher, so every once in a while a books is rental only or lifetime only. Everything is laid out on the product page and I've never run into any errors. Prices are competitive with Amazon and other retailers. Refunds seem to be automated, so as long as you haven't already read more than 20% of the book, haven't returned the same book in the past, and haven't already returned 3 books in the last 90 days, you can expect a quick refund. Sometimes books from certain publishers or delivered by the publisher cannot be refunded. This is all detailed in the return policy. The Bookshelf app --Features and Performance The Bookshelf app's feature set has stagnated in recent years, and I stumbled on this page because I was looking for a way to report feedback on how highlighted notes should have better UI, but the desktop and web apps are good and by a country mile the best DRM reader out there. It's even better than the Kindle app - step up your game, Amazon. As with everything else in life, there are some weaknesses. The desktop app is a memory hog. This might have to do with existing DRM protection implementations, but if not, performance in this aspect can be improved, and may be the reason users with lower end hardware face issues. Conclusion Vitalsource has a great marketplace and offers the best DRM reading app available today. They're not perfect, and the app has weaknesses that regular PDF apps like Adobe Acrobat or Readdle's PDF Expert don't have, but it has more than enough features and is stable enough to rely on for daily use. Well worth checking out if you prefer eBooks over paper copies.