My band uses the AX3 for practices in our rehearsal space, and for when we play live. Our songs stretch from: Standard, Dropped D, Dropped C#, Dropped C, Dropped B & Dropped A#. With that being said, we use one guitar in standard with the V.C. with the pitch tracking set to smooth and tracking at "1.0". We (2 GTRs & 1 Bass) can't detect that much of noticeable latency - both wired & wireless. Lastly, when we play live - the number one question we're asked is "how did we do that with one guitar" and the follow-up comment of "no shit, I would have never known you can do that". It's excellent and more than passible for live.
However, I feel the FM3 lacks the same type of quality with the V.C. I feel like the tracking is very sluggish and not as sharp. There are some artifacts that are present on the FM3 that aren't on the AX3. I would absolutely still use it live, and honestly, nobody would really know.
After experimenting with multiple units & plugins, this is my opinion on the best virtual capo / transpose:
1. Neural DSP's Plugins
2. AX3
.
.
3. FM3
.
.
.
4. Helix / HX Stomp