Studies have shown that at doses of 1u that pens are actually (surprisingly) more accurate than syringes. I’ll look for link.
I agree that a 0.5u dose will not be superbly accurate “slack in the system” – but it’s so little insulin that it doesn’t really matter much.
I have only used humalog a little bit, like 2 pens worth… but at the time my impression was that it was slightly slower than novolog, less of a peak and slightly longer overall duration, nothing insurmountable… and I’ve seen other people note different observations or no differences at all