Can tokkul be effectively spent on obsidian shields, or is it only worth it to save up for the onyx?

While gathering those its high chance that u get it as a drop, from those 143 lvl guards. And u get most obsidian money from them also. About onyx, its long way but if you have time this can be nice goal.

With the shield you get 3.489 coins per tokkul for selling it on the GE, whereas with the uncut onyx you get 5.259 coins per tokkul from selling on the GE (although you might want to seek a better street price).

With the shield you get 3.489 coins per tokkul for selling it on the GE, whereas with the uncut onyx you get 5.259 coins per tokkul from selling on the GE (although you might want to seek a better street price).

Adding to this, here's a link to a tokkul-gp conversion calculator:

 

http://runescape.wikia.com/wiki/Tokkul#Spending_Tokkul