For my personal use, I agree with Shooter. If I was limited on gear, I would have a PVS-14 on my melon and an IR laser on my rifle. If I wanted too, I could then attach a 3x magnifier and weapons mount it.
However, not everyone has the same use case scenario. Half the fun for me is just navigating with night vision on my head. I really enjoy that aspect of it. And if we are being honest, a lot of that is just because it is a strong reminder of times past for me, of a time when I was far more capable and far cooler.
A lot of my customers by a clip on first. A lot of people will gripe about that, but for some people, it's a perfect fit. If you just want to hunt over a feeder, have no desire to wander around aimlessly in the dark, or are covering a very specific, narrow area, a weapons mounted system is great. There are certainly safety aspects to be aware of in that use, but it is a great fit for some.
To more directly answer your question, if I was getting two devices, I would get a night vision monocular, and a light/small thermal clip on. It would let me navigate and shoot with the monocular, but I could also use the thermal clip-on as a hand held detection device any time I wanted, then throw it on my rifle for magnified shooting, once the target is positively identified and a safe backstop is confirmed. Then there is the converse. You want to cover more area, but don't care to navigate with NV. You could get a small thermal monocular and a night vision clip on. Then you could detect with the monocular, ID and engage at much longer distances with the clip-on.
It is going to come down to the way you want to use it more than anything.
