I got an A4 the last time it was on Woot & have spent way too much time figuring out what it can & cannot do. The final verdict is decidedly mixed. To sum up:
1. There are about a dozen different versions of what is basically a cheapo portable digital drawing pad. I believe the original is by Yifang (Taiwan, not PRC), which supplies multiple other OEMs, including the Wacom Inkling (at least I suspect that).
2. They share in common a sensor that clips to the top of a "page" (in the case of the Apen A5, the "page" is an iPad screen; the A1-4 is a piece of paper) & a pen that has a ring of sensors/transponders close to the tip of the pen. The sensor follows the movement of the pen's transponders to record what the pen has written/drawn. The sensor subsequently (or simultaneously depending on implementation) transfer information to a Mac or PC, or iPhone, or iPad, or Android device via USB or Bluetooth (the A3).
3. The sensor doesn't work w/ a legal pad, b/c of how the clip is designed - it can't attach to more than a few pages of paper - so you're forced to use loose sheets or a spiral bound notebook. The pen uses a replaceable ball point cartridge (the same as is used in multi-pens - widely available, not a great writing experience). I understand that some of these devices - the A5 & maybe the Inkling - are pressure sensitive, but the A4 & A3 definitely aren't. The pen requires 2 watch batteries. I don't know how long they last. The sensor charges via USB (but I don't know about the A3 which has bluetooth)
4. All in all, it's pretty clever technology for digitizing your drawings or handwriting. However, as you might imagine, the real issue is the software available on the host computer/tablet/smartphone.
5. I got the Apen4 b/c it seemed kind of cool (it is) & hoping to use it to turn handwritten notes, taken when I interview patients (I'm a physician) into digital text. The Apen advertising clearly implies that their device can do handwriting OCR. I also knew that the Mac (which is what I use mostly) has built in handwriting OCR (Inkwell).
6. I finally did get things working to my satisfaction, but it took 3 days of web searching w/ zero assistance from Apen. There were definitely points of time when I felt very ripped off. I could get the Mac built-in handwriting OCR to work when I used the Apen4 purely as a digital tablet, data entry device, although going back & forth between writing & mousing wasn't simple. There was no way to turn the remotely generated notes I took using the Apen 4 into digital text, however (despite Apen's advertising)
7. Fortunately, I finally found a workaround. Visionobjects.com has a Mac (& PC) program, Myscript Studio Notes, that is designed to work w/ all these devices & can import the note files produced by the Apen4 & do the OCR. It does a pretty credible job of OCR, but not miraculous: basically, if you can't reliably read what was written, the OCR won't work well, either. It does come w/ a training module, however.
8. Myscript Studio Notes has a 30 day free trial, but then costs $42.75 to register (which I did just do).
9. I fiddled w/ the iPhone a little bit, but the results were very unsatisfactory. I think the Apen 4 (& 3) does OK w/ creating images & drawings, but there was no way to do handwriting OCR. Vision objects has myscript notes, an iPhone/iPad/Android app but it doesn't work w/ the Apen hardware (you write w/ your finger or a stylus on the touchscreen, then the app sends the image to a vision objects server which does the OCR - just like Siri - this costs extra, of course)
10. The bottom line: Apen, the company, sucks, although I don't know that any of the other OEMs using the Yifang technology (eg Wacom) are much better in terms of telling you the limitations (btw, I strongly suspect that some of the glowing comments about Apen on Woot are plants). However, vision objects software does make the Apen 4 (I don't know about the A3) usable for digital notetaking. If you just want to digitize drawings & images, then the Apen isn't bad (although I imagine it wouldn't compare to a real Wacom table). If you want to digitize handwritten notes, you'll have to purchase additional software