As I have a set of mech pencils that include one of these, I thought I might add a comment on what I have found.
I have the following:
OHTO Super Pro-Mecha PM-1507P (.07mm)
GraphGear 1000 in .07mm
Rotring 800 also in .07 (can you tell I have a preferred lead size?)
All three have performed great for me (I have had the GraphGear the longest) but more often than not I grab the GG or the Rotring over the OHTO. The rotring is heavier and satisfyingly spring loaded when deploying the lead collar. The GraphGear is the simplest to deploy at one push (lead collar and lead deploy at the same time). The OHTO is a lot to fidget with (which also has its advantages in mech pencil). Overall, the Rotring feels like the most solid of the bunch and is the most compact. I have posted some pics for size comparison (including my recently purchased Lamy Swift - THANKS MASSDROP!)