I only use extended boluses either to cover slow adsorbing carbs and protein or to avoid bolusing more than 5IU at once (where I just do a half our delay on part of the bolus.)
For unpredictable food intake, not just grazing, but restaurants too, I do a nominal amount to cover 20 or 30g of food then another bolus later, e.g. when the main course arrives on the table.
It doesn't work to test because the Omnipod model of carb adsorbtion is broken; the PDM assumes it is all adsorbed instantly. I have my insulin action time set low so that I get a good result if I test and correct after a couple of hours, but if your insulin action time is set to the usual four hours you will find that corrections after 2-3 hours under correct.
So we really have no choice but to carb-count, however inaccurately, and bolus appropriately (without entering a bg reading!) If you test to check for low BG *don't* answer "yes" to the "use this for bolus calculations" screen, otherwise your blood glucose will go through the roof.
For low BG eat (and don't bolus), for high BG ignore it and just keep bolusing for what you believe you have eaten.