Yes you got me, i love to make boards. ;-)The new magnetometer is pretty flexible, it will let you (through a solder jumper) select 5V or 3.3V mode, it has a 3.3V voltage regulator and an I2C translator (translate the I2C signals to 3.3V to void damage to the unit), so you are free to use it with any microcontroller (normally you don't suppose to connect it to a micro-controller that uses 5V signals). In other words is the smallest, cheapest, 5V and 3.3V, 3-axis magnetometer on the market (yet).
Another feature is that you can remove the screw holes sides in order to keep the minimum size. If you don't care about the size but you care about holding it very well then just leave as is. My recommendation for ArduIMU+ and other projects is to place it as far as you can from the any magnetic interference, you can solder a long wire all way down to the magneto board, don't worry about the noise because the i2c protocol is digital (not analog) and also the "I2C translator" acts like as a signal booster. Do you want more?
For ArduIMU+ and future ArduPilotMega Shield owners the magneto board will be pin compatible, so you can just place it on top (as the upper picture indicates), without compromising the low profile of the board:
All this for just $49.90, the same price as the SparkFun board but with more feactures. Also it works under any circumstances, thanks to its bigger tantalum capacitor (33uF).You can get yours here:http://store.diydrones.com/ProductDetails.asp?ProductCode=BR-HMC5843-01If you mix it with the ArduIMU+ it will cost $25 more than the 9DoF Razor board, but just remember that ArduIMU+ runs at 16MHz, has GPS port and you can easily place the magnetometer away from the board in case you have noisy magnetic fields close to that board that normally don't affect the accelerometers and the gyros, also the 9DoF board has I2C accelerometer that i doubt is better than the analog one we have.The advantages of 9DoF Razor is that you have Lithium Battery port, ON&OFF switch, fixed mounting holes, is $25 cheaper and soon will support our DCM code. So is up to you! ;-)Thanks for all your support!