It's much smaller. That's about it. Compare the two: (use the mini usb plug as comparison of size)
M-1000:
http://www.buygpsnow.com/holux-m1000...mount-826.aspx
M-1200:
http://www.buygpsnow.com/Holux-M-120...ount)_897.aspx
I think it's worth 10 bucks to have a GPS that you can keep on your keychain and bring anywhere rather than a brick which you'll probably leave in your car. Besides, you usually get lost when you aren't expecting it right? You typically have your keys and phone right? So even if you aren't driving, if you're walking, or riding with somewhere else, you have your entire GPS system in your pockets. DEFINITELY worth $10 if you ask me.
Edit: Oh, you can't see the mini USB connector in that pic... hang on...
Okay, here you go, this is a similar picture to one I saw that convinced me to buy this one, sorry for the crappy pic. All I had was my phone and we all know how that works out. 
