What specifically are you looking to do?
Fusion/COTI is a somewhat different capability than a dedicated thermal scanning device like the Breach.
For starters, I wouldn't really recommend using either a fused system or Breach weapon-mounted, as neither is a thermal weapon sight.
Dedicated fusion versus the COTI/E-COTI has some pros and cons--but the major ones that will be applicable to your situation would be the ability to use dedicated fusion systems in a stand-alone thermal mode during the day if needed, whereas the COTI/E-COTI must be used through an NVD, as they are a front-projection through the tube, unless you get a stand-alone adapter.
That being said, a dedicated fusion system will be larger and bulkier, require a proprietary mount, and the device can't be removed when not needed. Also, since the fusion is integral to the system, if something goes wrong with the thermal, it could deadline the entire device versus a COTI system that would allow you to continue using your NV--thermals eat a lot of power compared to NV alone as well.
Also, the ENVG (except for the yet to be fielded ENVG-B) is designed as a monocular-only system, while the COTI/E-COTI can be used with a binocular NVD, though the thermal will only be projected into one tube. The L3 FGS-E is a binocular system, but will be even more difficult, and substantially more expensive to acquire even than an ENVG. Moreover, the ENVG more or less leaves you with a fixed thermal package that is under the NV monocular, which more or less rules out the ability to use an optic passively, whereas the COTI/E-COTI can be mounted to the side for a slightly lower-profile package (also stows better IMHO, which is why ENVG systems require an INVG-type mount, so the tall optic can be rotated out of the way).
Fusion/COTI/E-COTI is a tremendous tool--for what it was designed for, however, I would caution anyone to be aware of what it does, and perhaps more importantly, doesn't do before pursuing that route.
These systems are great for detecting potential threats, especially in urban/suburban areas and brush, and work particularly well for mixed-light scenarios where ambient/environmental lighting can affect your NV, but they work best at relatively close-ranges, and are designed to augment image intensification devices--your primary sense will/should still be the NV, the but the thermal adds an additional spectrum for detection.
Here is a short demonstration (admittedly not the greatest video) of the COTI (AN/PAS-29A: 320 x 240) in a mixed light urban area from our Armed Professional course last week during an "off campus" exercise focusing on movement techniques, where ambient lighting shifted frequently and rapidly from extremely dark areas, to brighter street lighting. You can see the difference in signature between NV-only, and Patrol and Outline modes on the COTI detecting concealed students:
Optics-1 AN/PAS-29A COTI
As you can see, it's a great tool for detecting potential concealed threats when conducting movement, while still allowing you to engage with the IR laser or passively through your sights, but it's modes are primarily designed to integrate with the NV--the full thermal mode (not shown) is rarely engaged by most users, and tends to have limitations compared to dedicated units, when it is used it is almost always in a static position--rather the Patrol and Outline modes tend to get the most use.
The E-COTI does have better resolution than the COTI shown, but again, it shouldn't be used in the same way as a primary, dedicated thermal device--it's an NV device that has thermal detection capabilities that can be used seamlessly with primary NV sighting devices and on the move.
Cost-wise, if fusion versus a dedicated thermal and NV is what you want, you could get a set of L3 Unfilmed WP goggles (RNVG, Sentinel, DTNVG, etc.) and an E-COTI and still come up on top of what the price of a single ENVG is--and IMHO, for what fusion works best for, binos are far preferable to a monocular, which is why fusion binoculars are at the top of the military's "wish list" at the moment. If you got MOD-3s, you could also run the monocular setup if you'd prefer.
The other big benefits of dedicated fusion systems are mostly Augmented Reality/Situational Awareness/C2 features like HUDs and networking/direct feed, however, you're unlikely to ever be taking advantage of those benefits unless you're being issued the system (the E-COTI will also support a HUD feature--but again, it's unlikely to be of much use without the right C4ISR systems tied in, making it a moot point for civilians and even most LE).
~Augee