After three years of buying machines and parts here I finally worked out a system for the points and codes that doesn't leave me feeling cheated. The trick is patience. The emailed codes and coupon exclusions almost always block anything alredy marked down, so I stopped trying to use them on filament bundles. Instead I hold the points and spend them on full-price items I'd buy anyway, like nozzles, spare boards, or that enclosure upgrade I kept putting off. Full-price item plus a decent code beats a sale price with no code almost every time. Second tip, put stuff in your cart and just leave it for a few days. I've had a sitewide code land in my inbox mid-week that covered the exact thing sitting in my cart, wich would never have happened if I'd impulse-bought during a bundle promo.
Also worth doing, message support directly when a code gets rejected at checkout. Twice now they've manually applied somethig or pointed me to a better route than the checkout page would allow. Takes five minutes and beats arguing with the coupon box.