I have the Leo. In fact I
reviewed it back in November. But I know very little about the Mach II, other than having watched Stephanie's (
Stepherz)
original and
follow-up video reviews.
The first thing to know about the Leo is that it is
not short: 153mm (i.e., penstyle length) – much longer than your 119mm 901. I don't know the length of the Mach II (there is very little descriptive information on the
MystMasters website). It
appears to be about the same length as the Leo, but 1mm less in diameter (which may make it appear longer).
I like the Leo, but the second thing to know about it is that it is not compatible with anything else. [I love the taste of the Leo atomizer and cartomizer, but their relatively high resistance combined with the battery's 3.5V doesn't give me as intense TH or vapor as I would like ... and there is no way to use them on higher voltage batteries.] Whereas I
believe that the Mach II is 510-compatible. This opens up a huge world of atomizers, cartomizers, and tanks that cannot be used with the Leo (other than with a $10
adapter, which further extends its length).
The
$65 Mach II seems to be the same as the less expensive
CRV 900 carried by Smok
Tek ($55 for a two-battery/two-atomizer kit), which definitely is 510-compatible. My sense of it is that it is a stylish eGo clone.