How should I spend my Shadow Orbs?

Title. I'm at Act 4 (Wasp act) now and spent some shadow orbs on a few medium-tier enchantments for my favorite weapons (Sai & Oriental Sabers with time bomb, Tonfas & Steel Batons with bleeding) and one medium enchantment on 2 armors. Here's the thing:

I don't know how hard it is to get these red orbs. I play mostly on Eclipse except when the challenge level is hot garbage like "fall = lose" "hot ground + red zone" then I switch back to daytime. How do I optimize my spending of enchantment orbs?