I have the Nano 2.0 , not the 3.0, but the 3.0 did not change the clamp.
I don't have any problem with maintaining temp, within 0.5 degrees F.
For a few steaks or chicken pieces, I use one of my Ninja Never Stick pots. I don't even bother covering it. For a larger piece like a brisket, I have used a 16 qt Sterilite Plastic tub. It does not have a lid, so I just covered the top with shrink wrap.
So far no issue with water level. It's been easy to shoot for something a bit lower than the max line. The app does work, but frankly it's easier to just use the top controls. If I have one small thing that could be better, it's a little bit noisey. Not terrible, but the larger units are quieter.