I've been on my new ML since it came in Monday morning's mail. It definitely has a better feel than the M, and appears to have fit and finish worthy of a $200 device. I had the first batch of M's and the paint was coming off within a day using my fingernail, but the finish on the ML seems to be baked on showing no signs of use after 2 days (passes the fingernail test). The recessed name plate is another nice touch and gives you an extra fingerhold for those with slippery fingers.
Functionally, one thing I noticed right off the bat was that I had to lower my temp settings vs the M. I had been running at 420 and dropped down to 400... also lowered the Joules from 30 to 27. Initial (subjective) observations are that the ML runs a bit smoother and does a better job handling SS316L than the M did. I think when pb puts up his scope pictures, it will show the stability improvements ... probably related to more accurate resistance measurements that the ML is capable of.
The battery cap is definitely better than the M's (deeper slot and wider threads) but still a bit sticky on the threads and slippery to turn with your thumb ... I've been through 6 or 7 battery changes and I may be running for a dab of dielectric grease on my next battery change.
Another thing I like (minor) is that the temp compensation now follows the F/C setting so I can set the compensation to room temp in F instead of converting to C. One thing to be careful of is that when you switch between F and C your old value is retained so if you set 19C and then switch to F, the compensation goes to 19F (not 66F) ... found that out the hard way
One thing I don't understand is why they bothered with Junior/Senior mode - to begin with the nomenclature is confusing, would be better with Basic/Advanced (or ADV) .... but getting past that, what's the point? From what I can tell, you can only get to the Power/Joules setting in Senior mode... Then if you select Power (Power vs Joules) you basically are in Junior mode and if you select Joules you basically are in Senior mode. It's like wearing a belt and suspenders and just adds another menu item to scroll through when I want to tweak a setting. Maybe the manual will shed some light on that.
For those debating on the M vs the ML, if you're running stainless or even considering it, subjectively speaking, I'd say its worth the extra $30-$40. Most likely the same for ti as well. And, even if you're not running in TC mode, you might appreciate the extra power, and the subtle improvements in fit & finish.
Looking forward to playing around with the software....