I'm still searching to find what are the differences between the two.
The operating principle on both is basically the same (rebuildable parts are similar, both have
juice control), Penelope is thiner than the Odysseus, Penelope is made for 14500 PVs (to be used with her husband Proteus) although it can be used with any 510 PV. Odysseus looks better with "fatter" PVs (as the GGTS). The one that was on stock recently was Odysseus short mode, it has minor modiffications to the rebuildable assemble in comparison with the first Odysseus version.
Just after the first version of Odysseus was released there was an Odysseus expansion set that included additional parts to use the Odysseus in different modes: Full mode (bigger
tank with transparent window), 510 Mode (to be used as a tank with 510 attomizers), E2 Mode (to be used as a tank with E2 cartomizers), dripping mode, etc. It came with 510 base connection but there was also available a native GGTS base that allow it to be used natively on the GGTS (with air flow control).
I do not know if Imeo have plans to make expansion sets and GGTS Odysseus base again.
There is some info in the GG Wiki:
Golden Greek - E-Cigarette Wiki
http://ggwiki.et.com.mx/index.php/Main_Page
Penelope:
Tank capacity: 3ml
Width: 17mm
Length: 45mm (without mouthpiece)
Length: 63mm (with mouthpiece)
Odysseus:
Tank capacity: 3ml (short mode with 510 base)
Width: 23mm
Lenght: 38mm (short mode with 510 connector base)