It uses M3. I'm liking it so far, although I haven't tested it over 200mW yet. Smart Audio is working fine. To be honest it seems like a bit overkill for a 2" build. The AKK Nano 2 is smaller/lighter and also has SA. I bought a Nano 2 and plan on trying it on my current project, a lightweight 3" build. The FX3 would probably be better on a lightweight 4" or 5" using a 20x20mm stack. Also, some people are having issues with the mmcx and ufl connectors coming off. AKK appears to be soldering the connectors on by hand with inconsistent QC. One of mine had almost no solder on the connector, and another had a huge blob of solder on one of the grounds. I would recommend checking the connector and possibly resoldering if it looks shoddy.

I'm very happy with the Omnibus F4 Nano/Ori32 ESC combo. It's a tad heavy for micros but should be just fine on a 3" build. In fact I ordered the same combo for my next build which happens to be a 3". As you can see in my photo I have the ESC with the pads facing up and battery pads facing the rear. I'm pretty sure for this orientation I just needed to swap motor 1 and 4 resources in BF. For the FC I kept it upright and rotated the board 180 degrees, that way the USB port is still on the side for easy access and the ESC connector is in the front matching the ESC.

Sure it's the orientation the more natural for this combo. Thank you so much for your answer and your photos.

Yup! haha. I've been using Velcro brand one-wrap thin ties. They come in 8 1/2" so I just trim to length. They're cheap (50ct for $4-5) and they are very thin so they slide under components easily. They hold very well, but they don't grip, so you definitely need something underneath to hold the battery in place. I use foam tape with low profile hook and loop on top. Once I strap it down it's solid.