First, you and I hate to spend money for convenience we don't need. In many / most situations DemonLite is a much cheaper solution. Got dual headlamps? DemonLite will cost you half as much. Willing to operate your modulator manually with a switch? DemonLite will save you a third, even if you have a single bulb headlamp?
Second (and this may not apply to you), we are DIY nuts. We would much rather do it ourselves and get it exactly the way we want it done rather than put up with expensive compromises. Take my ST1300 for example. I have it set up so that I can modulate the dual headlamps (on bright or dim), modulate the driving lights mounted down on the forks, or not as well as control whether they are on all the time or just with the high beams.
Third, you may what to modulate other forward-facing white lights, such as driving or fog lights (like I do) and the Plugn'Play stuff is just set up for headlights. No problem with DemonLite. In fact that is the easiest DemonLite installation.
So, want the convenience of Plugn'Play? Go for it. My competitors make fine products. But if you have an itch to make yours special and save some bucks in the process, step right up!