I think this is accurate: alto flute is good down to A below middle C; the G# and G are like C# and C on a regular flute, extensions, so they can be played and may have a good effect, but need special care (like no G-G# trills, no fast passages involving these notes, etc). Bass flute is a very rare instrument, personally I wouldn't write for it unless I had a bass-flutist who wanted the piece (and then I'd arrange a meeting with that person and go over their preferred range, no matter what the instrument is supposed to do!) I think the nominal range for a bass flute is an octave below a regular flute (so down to C in the bass clef). Alto flute is usually written as a transposing instrument.
Harp true glissando requires hitting seven tuned strings per octave; each one can be tuned a semitone above or below the note in a c major scale. Something like a B dominant seventh is therefore more easily achieved than a C 7. (C string = B, D string = D# E string = Eb F string = F# G string = Gb A string = A B string = B).
A harpist can make a good fast arpeggio, and it might sound as good or better than the gliss: four fingers per hand, one per note of the chord, covers two octaves of a 7th chord and can be played fast or slow, loud or soft, and with good control.
