I have got a Canon Pixma ip4200 printer, the model before the 4300, and i can only say that it is a very good printer. The automatic duplex printing (printing on both sides of the paper) does sound handy but you should know that if you are doing duplex black printing on plain paper the printer may not use its large black tank of pigmented ink. (Which it normally uses in economy mode on plain paper) Unless they have changed this, like the 4000 and the 4200, it will use its small black dye-based ink instead in duplex mode so you may find that what you save on paper you spend on ink. Of course to get around that you can always do manual duplex printing, like you can with any printer.
Manual duplex printing is where you first print the odd numbered pages, 1,3,5,7 etc and then you take the stack of printed pages and put it back in the printers feed tray facing backwards and then you print the even numbered pages 2,4,6,8 on the backs of the already printed pages.
I am still glad I got this printer though. It has very good paper handling, and the cassette is a nice feature. I do not traditional sheet feeders that poke up from the top of the printer where the paper can curl and get creased. The ability to print on CDs and DVDs is very handy. USA models have this feature disabled for "legal" reasons. The RIAA doesn't want you guys doing this. But you can legally order the CD tray from Europe or another free part of the world and reset the printer's "zone" using front panel button press sequences. Google will find them for you.