While your iOS device is on the Dock connector, it's getting charged. The projector is able to pump out an image from any iOS app that supports video out, such as Keynote, YouTube, or the Photo Library. Unfortunately, like most devices that support the Dock connector, the MG-850HD doesn't work with the video mirroring capabilities of the latest iPhones and iPads. You can connect via an HDMI cable (not included) to use video mirroring, but not through the Dock.
During a presentation today, I used the iOS version of Keynote to deliver the presentation with my third-generation iPad plugged into the MG-850HD. For a remote, I used Apple's Remote application on an iPhone 4S. The iPad, which runs on Verizon's 4G LTE network, was used in Personal Hotspot mode to connect the iPhone remote to the iPad host.
The MG-850HD provides extremely bright output. Our presentation was done in a large conference room using a wall as a screen. While I had no way to measure it, the image was probably a good 18 feet wide and about 10 feet tall. Even with some lights on in the room, the image was clearly visible, and all of the graphics looked sharp.
One very helpful feature we used was the set of two built-in 10 Watt speakers. Since the presentation didn't have audio, we connected a mic to the audio input and use the speakers to amplify our voices to a large crowd of students. In a pinch, you could use the MG-850HD as an audio speaker dock for your iPhone without even using the projector.
The MG-850HD comes with a bunch of pre-set color modes. For home, there are special settings for "living room", cinema, and game, while for businesses there are special color modes for presentation and blackboard. The device can take just about any composite or component input signal up to 1080p in addition to the HDMI, VGA, and Dock inputs. The native resolution is WXGA (1280 x 800 pixels), which means that the HD projection output is limited to 720p.
When the projector was turned on and the iPad securely situated on the Dock connector, a "Dock" light illuminated, and a special menu screen was displayed on the screen (wall). Depending on the type of image (still or video) you're projecting, you make a menu selection and then press continue. One concern is that these settings must be made using the included remote control -- if you lose the remote or your batteries die, there are no controls on the projector as backup.
There are two very nice security features built into the MG-850HD for instructors; first, there's a standard Kensington lock slot for locking the projector to a heavy piece of furniture. The second is that you can set up the projector to only "unlock" (become usable) to certain iOS devices. You place a device onto the Dock, go to a hidden menu that is only described in the user manual, and then select "iPod Management". Once that's done, pressing a few buttons will display a confirmation screen that asks if you want to register your iOS device. Selecting Yes and pressing the Enter button on the remote control auto-fills the projector's memory with the device serial number. From then on, the projector is only usable with devices that have been registered.
In terms of portability, the MG-850HD rocks. I've used a lot of projectors over the years, and this was one of the lightest big-screen projectors that I've ever had the pleasure to carry at just 8.6 pounds. Size-wise, the projector is just 11.5" x 13.4" x 5.1" and could easily fit under an airplane seat.
It's obvious that Epson expended a lot of time and effort into making the MG-850HD work well with Apple devices. This is a projector that can be used in both home and business environments to view anything from iPhone slide shows to HD video from a Blu-ray player, and do it well. The price is also fairly reasonable -- a few years ago I purchased a much less capable projector for my business from Dell that cost quite a bit more and broke after only two years.
You don't have to take my word for it; the reviews online are equally as happy with the MG-850HD. Whether you need an iOS-compatible projector for work or play, the Epson MegaPlex MG-850HD is an excellent choice.