UTM-x is not a "clip on" ... while it can be used as such in an "emergency" ... that is not its design purpose. It has no collimated risley prisms on the rear lens assembly like real clipons such as PVS-30 or UTC-x. UTM-x design purpose is thermal monocular (spotter) though it can be used as a thermal scope in a pinch.
Repeatability is more a function of the mounts and mounting process. The wilcox mounts are generally famous for their wobble.
Further the old, original manufacture BAE OASYS units have no warranty coverage. The OASYS program was shut down in 2017.
Also, TT 5-25x is a tall order to put a thermal clipon in front of ... most thermal clipons are stretched to even get to 5x much less beyond.
The old FLIR T-75, the new LWTS-LR (which might be available in months to years), the old BAE UTC-x, the olde N-VIsion Optics TC-50/TC-50a can do 8x plus support on the day optic, but all those are virtually impossible to find ... aka "unobtainium".
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If you want to night hunt, another option is to get a second rifle and put a dedicated thermal scope on it. That's what many folks are doing, such as the Trijicon Electro Optic units or the new N-Vision Optic HALO units.
And for a lower price range, there are the Pulsar units.