For most people, a clip-on is not a good choice.
I considered a PVS-30 in front of my ACOG but, ultimately found a NV scope on a QD mount was a much better solution. Good mounts hold your zero and you end up with less weight and length.
When shooting from a fixed position, a clip-on is more useful but, walking around and shooting from improvised positions, I find the extra weight that far forward to be bad for "my shooting" and physical conditioning. Add a suppressor and QD mount, and the weight out front becomes significant which plain and simple sucks big time! The center of gravity between my hands lets me track moving targets much better yielding much better results in the field in my case.
That being said, something like a PVS-30 fits much better on my heavy bolt actions (9+ lbs) and lets me use day optics at night. On my auto-loaders, it just destroys the handling qualities IMHO.
In terms of using them as a scanner, eye relief and field of view can be problems so, consider your use case carefully against the specific tech specs of any potential clip-on acquisition.