The original HTC One works with HTC's own "Sense" user interface, while the Google Play edition works with Googles' - MoDaCo.SWITCH allows you to choose which of the two you like better at any given time. This system is a hack, at heart, requiring that you root your device before you allow yourself the freedom to choose either the HTC Sense or Android Jelly Bean Vanilla iteration at the tap of a button (and a few seconds' wait). What you get, though, is a completely unique set of controls.
This system is not just coming to the HTC One - currently in Public Beta, at this point, mind you - but the Galaxy S 4 as well. The Samsung Galaxy S 4 is one of two devices - the other being the HTC One - to earn itself the right to be a Google Play edition in addition to being its own Samsung-made self.
What the folks at MoDaCo - just one fellow, that is, ROM developer Paul O'Brien - will be doing is adding an on/off switch to the full ROM of all the little bits and pieces that make up Google's edition of the software right next to HTC's version of the software. Whenever you'd like to switch from one to the other, you'll have to hit the reboot button, but all of your data will be safe and sound flipping back and forth.
Now we've only to wait for this same sort of system to appear for any and all smartphones on the market with their own custom UI over Android. Could such a toggle switch be added to Android as a requirement from Google in order to be Google Certified?
Such a thought is quite intriguing, to say the least.