Speartip sharpener

Hey guys, im a real newbie to this sport so this may not even be an issue for many of you.
Ive been looking everywhere for a sharpener i can take with me out in the water that makes it a little easier than just a normal file that has to on the boat.
The little poolcue chalker style ones dont seem to get a good review so i saw this diamond file with a groove up the center.
Drilled a hole in one end for a lanyard and has a good angle for the tip ( in my ametuer opinion!)
Havent tested it yet in the water but i hit the spear on a rock and resharpened it no worries.
Thoughts ?

Cheers man i see your point and yes i would say my skills definitely need improvement!
Though we do hunt around alot of rocks on the south east of aus and originaly with the tri cut factory tip i was sharpening every trip, one bad shot would blunten the tip so if we had gone out from the beach it means a long trip back sometimes!
I wonder if spear quality has alot to do with it as well?
I have an ocean hunter chameleon, and i imagine for the price it would have lower quality materials with it.
Also only using one band at the moment means a blunt spear shot that hits the spine on a few occaisions has meant lost fish.