Personally I adopt a suck it and see approach similar to yours. I estimate the carbs in the meal I'm about to have and take my insulin for that. Sometimes I will take a unit less before the meal and adjust with an extra unit or two an hour or so after the meal if I see my levels going up rapidly (via a libre so not sure if you have one of these). I would say if in doubt, take less than you think you will need as you can always adjust it later if you go high. Don't take more because you will then run the risk of hypo'ing. You have to be careful in knowing what you are doing but I pop in a unit at various times during the day when required, ie when I have a biccie or whatever. You have to be aware of 'stacking' though.