If you can spend some timd in the field hunting with someones gear, do it.
1. Unlike conventional optics, I am constantly pushing buttons on my thermal and NV. The clip on models place those buttons further forward than the old adjustable objective.
2. If you can dedicate a rifle to night hunting, just commit and buy thermal or NV. Strongly recommend the integrated rangefinder and now they have internal ballistic. Slick. If clip-ons don't have this, think hard about it.
3. Getting out will help with decisions. For instance, I could be persuaded that a handheld thermal for scanning paired with a high-end NV would be the way to go. A thermal scanner is a great tool to have in your kit. Plus, it is so much easier to scan with a handheld than trying to ride a tripod mounted gun with thermal.
4. Biggest downfall to NV I have seen is they don't work well at night in any kind of cover.
5. Identification with thermal is a learned game.
6. Thermal is thermal day and night. NV is actually pretty useful as a daylight scope in a manner very different from night hunting. (No illumination-so you don't have the issues with cover)
Hope this helps.