Oyster, the Peter Thiel-backed startup that aims to be a Netflix (s NFLX) for ebooks, was iPhone-only and invite-only for its first six weeks. On Wednesday, though, Oyster launched its iPad (s AAPL) app and opened up to everyone. And it is now offering a free 30-day trial of its service — which is essential, since consumers are still very unfamiliar with ebook subscription services.

When I reviewed Oyster six weeks ago, I was impressed by its design and its offerings — over 100,000 in-copyright ebooks for $9.95 a month. But I thought the app’s lack of availability on iPad was a big drawback because I think it’s hard to do serious reading on an iPhone. The launch on iPad remedies this problem, of course, and subscribers’ books will sync between both devices.

Oyster’s design on iPad is great, just as the iPhone app design is. One feature…