i will go through a first rough impression and then you can tell me on which part you might want more details

so, first of, 1.3 vs 1.5:
-both use flash memory, thus safe wink
-1.3 has arps in all channels but only specific notes, 1.5 has arps in some channels but you decides on the notes
-if you plan to use it on a dmg or pocket (or light), 1.5 has an additional voice (yes, a fifth) which can add some nice detuning etc but is not really versatile. I really like it to 'drone' my pulses...
-1.3 has the retrigger function on the S channel
-1.5 can produce strange noises if you play with extreme sweep values on empty shells

now, the oldies(<1.3):
-they all sync differently than the newest, but still syncing is possible
-they all have trouble with complex sequences which adds character in my opinion... smile
-in all, playback is affected by d-pad pushes, like classic trackers, which can make interesting live things...
-the sound in all is more...DMG smile more harsh, it kicks harder and grinds sharper tongue
-battery based memory...thus risk of loosing tracks is constant.
-could be overly unstable and crashy
-have only 3 channels (n, s and double voiced p)
-<1.2 have only one S wave and the other 15 are derivates of the one you draw

...probably more differences exist, but these i think are the main you might face...