Yes I do use half unit needles. The problem is with the top of the bit of the syringe you push in. Its often slightly diagonal, It has turrets, and its rounded not flat.
I cannot find another needle that is 13mm long and has half units, whose size is 30 unit capacity. So unless I change to 8mm this is what I have to contend with. I used to give him so many fur shots and I feel safer with the 13mm.
When it is a unit or half unit I can gauge because there is something to see an exact point of the pushy part against.
When it is a .25 and I am in the middle of space, so to speak, there are so many different things creating warps in perspective (the turrets - which are random, and the curvature of the top) and this is why they are so hard for me. So I feel its more accurate if I can aim for either just under or just over a .25 - like a fat or skinny.
Clear as mud?