Are the UVA/UVB claims on cheap reptile heat bulbs trustworthy?

Generally no. A recurring point in specialist communities and reptile-lighting groups is that heat output from these budget bulbs is fine, but their UVB claims are not independently verified by the testing groups keepers rely on. For genuine UVB, most experienced keepers recommend a dedicated, verified UVB tube rather than relying on an all-in-one basking or LED bulb.