Brian,
I kinow this thread is old but I was wondering if you ever purchased this MK3?
To answer your (and maybe others) question, the Farallon MK3 is an old scooter (Farallon calls anything that is not a "ride on" a scooter... only if you sit on it is it a DPV) that was produced from the late 1970s through the 1980s. It was a popular model and is quite rugged (the body is made out of aluminum).
Farallon could be considered the "father" of recreational DPVs in that they have been around for so long (almost every DPV you have seen in a Bond movie during the 1970s and later has been a Farallon).
People tend to downplay them due to age, weight and the current company (only the MK7 and MK8 have been produced by the "new" company) but all things are relative.
As for how a MK3 relates to a Mako, the latter is certainly lighter in weight but the battery time is roughly the same. The MK3 will give you a deeper dive depth (gotta love aluminum).
Regards,
Ltstanfo