It depends on how you intend to use it/them.

I’m generalizing a bit, and it’s hard to put into concrete words, but for “long(er)” range use and tasks like driving (flying), ANVIS excels.

For closer work, especially with some ambient light, I prefer single.

We have both and, for example, if someone is tasked with driving, they drive with ANVIS, then switch to a 14 for “tactical” work.

ANVIS are harder to look under/around (the sides) so you’re committed to primarily tubes only; no help from your unaided eye.

Rarely is the environment zero illum, and being able to reference things with an unaided eye is beneficial for close in work and tasks like walking and negotiating obstacles.

Obviously, this is a sliding scale from binos are perfect to a single is perfect; where you fall in the scale is up to you to determine.

Anvis-9s are not the ideal system for most folks but they can make for a good entry level dual tube goggle at the right price.  

The biggest reason they are not the ideal system is because they are relatively fragile for ground use.

They require an ANVS helmet mount (plus battery pack) and the objective lenses can only be re-used with a limited amount of housings. The objective lenses filter/block green color wavelengths which may or may not be important to you and they also lower low light performance slightly (make for a darker image).

Many users who break them end up having to purchase PVS-14 objective lenses when they upgrade their housing. You will also need to purchase a new helmet mount if upgrade to a dovetail housing which most are.

If you liked the ANVS ball-detent system, the TNVC-BNVD-M (Artemis) is the best housing to upgrade to. You can also swap the Artemis' MPS (Modular Power Supply) ball-detent (aka ANVS) / dovetail (aka BNVS).

I didn’t even think about the fragility factor, although they are fairly robust.

Ours get inspected all the time and if you break something you just get a new set.

If I had to pay for them I’d probably have a different POV.