Even with a bowl, nonclimbing roaches are an option. I use one twelve inches across and three or four inches deep, so the toad can jump right into it, and even full-grown death heads rarely are able to climb out. Discoids would certainly be trapped.
I like bowls. You can use naturalistic substrate more safely than with crickets hopping all over, and there's no stress from uneaten bugs crawling/ nibbling on them. The toad gets to approach them on its own terms, whenever it chooses to. So what food items have you offered?
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0.1 Coastal Carpet Python (Boots)
0.1 Western Hognose Snake (Bebe)
0.1 Cane Toad (Hengo)
0.1 White-Banded Sheen Skink (Minerva)
1.0 Northern Diamondback Terrapin (Queequeg)