Its good, very good.
There is a bit of a learning curve, not really much in menu's but you have to remember different things.
Pushing the power/mic knob brings up transmit things menu and its mode dependant.
Fidelity is fantastic out the line output jack, the built in speaker not so much.
AM and ssb modulation is very good, set the TX bandwidth to 50 to 4500 on AM and there you go, no splatter.
Eq the microphone, it really works and it sounds good.
The built in monitor works fine, rx audio is great, dial the filter to whatever width the signal is on the scope.
High fidelity if you want it.
The screen is big and very high res, looks like a 4K TV.
Touch and drag the scope anyplace in the band without changing your receive frequency, listen on 7290 but look at the cw portion of the band.
Slide to expand or contract the spectrum display, its got calibrated markers on it.
You can have two receivers, on any bands and look at one, the other, or both.
I worked Tim (HLR) with it on 40 meters and he said it sounded good even using the hand mic.
He knows good audio.
Delay through the standalone radio is about 200 ms on voice, not enough to bother me, in the monitor there is no delay.
I expect less delay if you use a computer and run the software over ethernet.
It seemed fine on CW, sidetone was nice, t/r switching was fast and quiet.
You can use the standalone radio, you can buy another front panel and operate the radio over wifi, or from any internet connection, or from a tablet, or a phone.
The seperate front panel (Maestro) has built in batteries, jacks on the back for phones, speaker, microphone and other things, and works over wifi or copper. You can have both I suppose.
AM is not an afterthought, it works great, has options you want, and does not seem fussy, you really have to crank the mic gain up to get it to sound bad.
All the other modern radios like the 7300, the 7610, the ftdx101 and the TS890 have AM limitations.
The Icom's cut the audio off at 200 Hz on rx and limit the tx to 3000 Hz.
The ftdx 101 has a 9 KHz rx bandwith only and the passband tuning does not work on AM. I am unsure the TX bandwidth.
The Kenwood has roofing filters that might limit things for AM.
Some radios have fixed filters, you can not just vary them with a knob. Some do not show the filter width on the display, so no setting the filter
to the width of the signal exactly.
Flex seems to get sdr and AM.
Seems good on CW, at least the simple slow stuff I would do.
Its very easy to vary the filter to fit any signal or space.
The 6400 series is high up on the Sherwood charts with very low phase noise and good filter performance, but it may be at the top of the chart for AM operators.
Its nice they pay attention to how the radio works on all modes.
Hard core CW or contest people may have something to beef about, I don't do that so don't know, but the 6400M seems like a well working radio to me, easy to set up and operate out of the box, no need for a manual for what I do with it (so far), seems good for the price, it has enough ins and outs to do what you want.
A very positive initial impression!