Not quite as effective as benzos but more effective than say alcohol or diphenhydramine.
The problem with z-drugs for comedowns is that they are highly selective for the alpha 1 subunit of the GABA-A receptor, which makes them highly sedating but not so great in reducing anxiety (their hallucinogenic properties could even compound the problem). Most benzodiazepines have significantly greater affinity for the alpha 2 subunit which means they reduce anxiety more than z-drugs.
That said z-drugs still reduce anxiety. Only risk would be a high dose of z-drugs (say 30mg or more of zolpidem) combined with residual stimulants in one system, may result in some bizarre behavior, like driving intoxicated, black-outs while ambulatory, etc.