I just bought a used 424 and love it. I think you should look at what you plan on doing with the unit and buy the unit that fits your needs. I know it is hard to decide when you don't really know what the different units offer. I went to the Tascam site and this site and printed all the information, reviews, and specs. I think you will not "out-grow" the MKII as quick as you would the other. But the unit is alot bigger and less portable. Hope this helps. I would also check the warranty of the "Factory Rebuilt".