You can use your libre to figure out when to inject - so inject and wait until the graph starts to curve down, indicating insulin is working, then eat - but if you do that you have to bear in mind that the libre is testing interstitial fluid, which runs 15-20 minutes behind what your blood sugar is doing, so you don't what to be starting off your injection at too low a level and you will need to be ready to eat right as the curve hits - you can't really leave it another 5 minutes or forget once it's started dropping or you might drop too low and hypo before you start digesting your food, which will, frustratingly, undo the aim of the prebolus and cause a spike anyway because you will either have to take on additional carbs to treat the hypo or the hypo will cause a liver dump and spike.
That's a really long (and poorly punctuated) way of saying; pre blousing is good to reduce post meal spikes, but cautiously experiment with it to find the best way of getting it to work for you. Hopefully the libre will be a really good tool to help with the experiments.