VDJ was my very first DJ software (followed by Traktor → Serato → Engine) and albeit I never got truly warm with it, I have to give the Atomix team mad respect for their swiss-army-knife level of hardware compatibility. Not only in terms of quantity, but (often) also in quality. For example, great native screen support for all Engine devices.
Still, Serato comes with the big pricing advantage when being bundled with a well-priced hardware. For example, the €1111 SC Live 4. The included Pro license (and the fact that I once snatched P’n’T for $19) was my big deciding factor to make the switch from my former DDJ-SX/Roland-DJ808 (back*) to Denon. Until I fully began to embrace the full standalone way of life, it felt great to have an equivalent to Rekordbox Performance mode, something I still think EngineDJ could benefit from.
Overall it’s convenient to have some plug-and-play DJ software included for situations, where you need extra features (video, DVS…), or simply a larger screen. I tackle complex weddings with my Prime 4, but only because it’s 10.1" screen still has a reasonably size GUI - with a SC Live or Mixstream unit alone, I would feel far less comfortable, and I can understand similar concerns some people have in terms of the System One with its vertical 7" screen. So again, having Serato included, now with proper ‘hot swapping’ rather than cold reboots, is great. Getting more options never hurt, of course…
*) I had actually owned the lovely little MC6000, the surprisingly well-rounded DNX600 mixer, and two lovely SC2900 decks, at various different times during my quite turbulent DJ life.