odd, I replied to this yesterday... but some network glitch ate my response
the extended form is identical to the non-extended form, except it allows a range to -127 to +127 as input rather than the normal -64 to +64. (the actual table used by both runs -127 to +127).
its used since its common to sum inlet and parameters. (i.e. the param is used as an 'offset'), you don't have to do this, but this is the convention.
MTOF always (perhaps misleadingly) gives you phase increment, not frequency, but you can obviously calculate the frequency from it.
(however usually, you actually want the ph inc anyway)