It's surprisingly balanced for its build with only two ingredients but it needs the vinous tones of vermouth to become balanced like a Negroni. I do like the idea of it as a shot though. It's such a unique flavour combination to work as a shot but as a drink it's slightly off balance.
To supplement a previous comment - I like the M&M, but wanted to try other amari - see my comment below. I tried Aperol - good, but think the Aperol thins it out a bit too much at a 1:1 ratio, so I'd try 60:40, or maybe 2:1 Mezcal:Aperol. I also tried Romana Amaro (strong tangerine/citrus note) - it was ok - the Romana overwhelmed the Mezcal - I'd definitely need to cut back the Romana Amaro to about a 3:1 ratio.
I like mezcal and I like amaro - so this concept was very appealing. I tried the M&M recipe and was struck by how the combo brought out vegetal notes that I don't get from either ingredient in isolation. Very nice, smoky and vegetal and some sweet - I liked it. I also like rabarbaro amari, and so I tried this with Sfumato as the amaro (Sfumato overwhelms the mezcal - becomes a larger glass of Sfumato - not recommended). I am filing another comment with other amari notes.
Tried the Monténégro version which was quite nice. The obvious pairing for me was Cynar - vegetal, intense, bittersweet. Worked much better in my opinion. Used a Meyer lemon twist, which is a cross between orange and lemon. Perro de San Juan mezcal. Delish!
I used Del Maguey Vida mezcal. maybe good as a shot, and it is definitely an "interesting" drink...but like some previous reviewers, I don't know that I'll make another on the rocks any time soon. feels like a really good idea that needs something to balance it out.
Gary Walther's suggestion of Nonino plus orange bitters/grapefruit twist might be a better drink for my palette (though I do love Montenegro in other drinks).
I have always liked the Reanimator (equal parts Amaro Nonino & Rye), so I used Amaro Nonino here along with Del Maguey Vida. I think the combination is great. I added a dash of orange bitters as suggested by another reviewer plus a grapefruit twist. Delicious.