I don't have time to write up a full report (plus I don't remember specific usability heuristics offhand), but here's some feedback:

Installed by clicking on link to .apk in mail client, which downloaded
to phone.  Then clicked on .apk file in notifications listing to
install.  Much easier than the instructions on the wiki :)

Volume control alternates between media volume and ringer volume on
each button press, making it difficult to adjust the app volume.

Adjusting ringer volume (in attempt to adjust app volume) often causes
the phone to reboot.

Initially pressed Play immediately after recording, and then realized
needed to rewind to start first.  It's clear what happened here, and
it's possible this is the right behavior, but it was unexpected.

Autosave was useful, since song did not disappear after unexpected
reboot.  Oh, song did not actually autosave -- autosaved song was
empty.  Why bother saving an empty song?

"Rename", "Save As", "Export", and "Delete" buttons have only partial
text visible.  Buttons take up too much room to conveniently open the
song itself, since you have to tap the rectangle while avoiding the
buttons.  Perhaps add as long-press options, but sometimes long-press
options are hard to discover.  Or add as menu, since there are no menu
options (although then you have to figure out how to identify songs,
perhaps with checkboxes instead).

Only some tracks seem to play, and only some of the time.  Sometimes a
track will show up, and only the first several seconds will play.

When recording green track, red track played.  However, when recording
yellow track, no tracks played.  Similarly, when playing blue track,
no tracks played.

The Rename, Save As, and Export buttons doesn't do anything.

When editing, it was initially confusing how to do anything, since I
was swiping to lengthen the note, and it was already at its maximum
(because the track already existed to the right).  Also not clear that
you can't just tap the up and down arrows, because it looks like
swiping is for horizontal movement only.  Maybe allowing tapping too
would be useful.  "Tap anywhere" isn't quit true either -- it looks
like it has to be tapping within the blue rectangle.  Not initially
clear why there are two sets of left/right arrows, but it becomes more
clear when actually trying it.

Delete dialog says "Are you sure you want to delete this s..."  Ah, it
turns out this only exists in portrait mode.

Not a UI problem, but delete animation with song sliding to the right
seems cute, but then I would have expected the remaining songs to
slide up, rather than just re-displaying.

What's the difference between Export and Save As?

Pressing the on-screen back button triggers a save prompt, but
pressing the hardware back button doesn't.  These should be
consistent.

Song saved popup when saving during back seems unnecessary.  Saving
when explicitly pressing Save button seems possibly reasonable,
although is inconsistent with desktop applications which don't have
significant visible feedback when saving (although sometimes there's a
blip of a progress bar).  I suppose feedback is good, although a popup
might not be best.

When phone screen went black while app active, phone could not be
reactivated.  Had to remove battery to reboot.  Tried reproducing only
once, and was unsuccessful, so possibly unrelated to the app itself.

Seems like a potentially useful app, but a little hard to actually
tell without actual audio recording.

Untitled counter seems to persist, even if other lower numbers are
deleted.  What happens when numbers get very large?

Can't actually set a title, but I suppose this would be fixed if the
Rename button worked.  Perhaps prompt for a name and don't save
anything as untitled?  Although then a solution for duplicate names
would potentially be necessary.

Allowing copying tracks might be useful.  Maybe that's what Save As is supposed to do?

Might be useful to allow selecting/deleting sections, but maybe that's more functionality than actually necessary.