After a lengthy App Store approval process, the Readability app has finally found its way onto iOS devices. Readability is a free service that saves webpages for reading later in an easy to read stripped-down format. While it is new to the App Store, the service has been available through browsers for three years now, and is well known in the field. It's integrated into a lot of apps already, and parts of the code developed by Readability power the Reader feature in Safari. We've had a week or so to put the app through its paces and find out if it deserves pride of place as your go-to client for iOS reading, or if it's just another app in an already crowded market.

While Readability is technically capable of functioning as a standalone app using its built-in browser, for the best experience you'll want to use it in conjunction with your desktop or laptop. The Readability plugin is available for Safari, Chrome, and Firefox, but any browser that supports bookmarklets will be able to offer the basic functionality. The plugin enables you to add to your Reading List, read on your desktop, or send a webpage to your Kindle. The first thing that greets you upon opening the iOS app (after creating a free account) is the Reading List, the heart of the app, which contains all the articles you've marked as "Read Later," either through the aforementioned plugin, the in-app browser, or from links sent to your Readability e-mail address. There are also a host of apps which can save articles to Readability, including Tweetbot, Twitterrific, and Reader.

The app's interface is clean and simple, but there are some really nice UI touches that help set Readability apart from the rest. When in the reading list sliding a stub to the right reveals a set of options underneath, and tapping on an article has it slide in from the right. Once you're in an article you can slide the page to the right and browse/switch stories using a second finger, or flick it away to reach the main page. Scrolling past the bottom of the article loads up the next page on your list, and in-article options are neatly hidden by default — a tap of the screen brings up a bar along the bottom which also provides access to the (again beautifully designed) formatting menu. While none of the UI features are groundbreaking, the developer Teehan+Lax has clearly put a lot of thought into how to merge together all the separate elements into a cohesive, enjoyable, and compelling user experience.

Things aren't all perfect however: there are a few features we'd have liked to see, namely line spacing options, an in-app brightness setting and the option to split long articles into pages — three features found in Readability's main competitor, Instapaper. The developer has explained that pagination wouldn't work well with the swiping and scrolling interface, but one wonders if the trade-off was worth it.

Speaking of competition, Instapaper has been at the top of the pile for 3 years now, and doesn't really do much wrong. It offers a much richer discovery service, including a section to help you discover the editors' favorite pieces, and also enables simple discovery of your friend's favorite articles. Discovery is a huge part of what makes Instapaper so popular, and the lack of any similar service from Readability could be a major sticking point for potential users. Instapaper's weak point however is its interface and formatting, especially on the iPhone. We've found articles to be formatted incorrectly on occasion, and stray sentences and erroneous codes are commonplace. In contrast, Readability failed to render only one page correctly, and after e-mailing support (from an anonymous account), the page formatting was fixed within 24 hours.

Readability and Instapaper have a long history together — the two services have co-existed peacefully since their inception, and the company's first attempt at an app was actually developed by Marco Arment, the creator of Instapaper. The first app was rejected by Apple over a year ago as at the time Readability was a subscription-based service, which contravened Apple's App Store policies. The new app was developed independently, but it appears there's no ill-will between the two services: Arment blogged about Readability's attempted re-entry to the App Store back in November and concluded that "there's no reason why we can't respectfully share [the market]" adding that he hopes to remain friendly with the creators.

As it stands, Readability is a pleasure to use and offers one of the most polished experiences we've had with a third-party app. It's difficult not to recommend the free app over its paid competitor, unless you're really keen on Instapaper's discovery features. But if, like many out there, you've already paid for Instapaper or an alternative app, we're not sure that Readability has done enough — yet — to persuade users to migrate to their system. However, the app is free to download from today, so if your interest has piqued, head on over to the App Store to give it a try.