All last summer I was using a 14.4V battery drill fitted with a sawn off ball ended hex allen key.
However in winter cold weather, and maybe with my motor a bit more worn, it doesn't tuurn the motor fast enough to get it to start easily, which is a pain.
I have a 12V conventional starter and it drives me mad becuase always the damned thing wobbles out of the rubber cup.
I just did a similar mod to you, tapped the end and loctited it tight on the sahaft but after 3 starts it came loose. So now it has been drilled and a roll pin put through to fix it on forever.
The starter has an old 450 1800 3 cell lipo velcroed to the side. I have a selection of old 450 packs that won't fly the heli much but are still good for a few starts
My wand as no one way. There is a one way in the heli start shaft on my raptor and 600n so I see no need for a bearing in the starter too.
I've not really tested this setup much, but I jjust don't like spending money on stuff like sarters (but the heli, 600n pro, 3xBL451, CSM720/BL251 maniac 603, is a different story!).