No you are not reading it quiet right.
You CAN buy a weapon that is not meant for that specific character and that weapon is bound to legacy and so can be mailed to any other character back and forwards etc. However if you earn say 3 grey helix with one character and you have 15 on another you CANNOT mail THEM so that one character has all 18 and which would allow you to buy a weapon.
If the event was to finish outright you'd just be stuck with useless tokens.......a bit like the useless Reputation tokens I get while trying to earn the grey helix as I have the Legend Reputation already. I just have to dump them.
The one good aspect I suppose is that the weapon is legacy bound - its a shame though that they didn't make the mount and the grey helix tokens legacy bound too. I'm guessing that the reason for not doing so was to keep people coming back to the missions over the year otherwise I'd be well shot of Ilum at this stage.
Ok, thanks for clearing that up. Was worried for a moment. And I agree that they helix should just be BoL since it's used to get BoL gear