flaky

adj. (var sp. flakey ) Subject to frequent lossage. This use is of course
related to the common slang use of the word to describe a person as
eccentric, crazy, or just unreliable. A system that is flaky is working,
sort of enough that you are tempted to try to use it but fails frequently
enough that the odds in favor of finishing what you start are low.
Commonwealth hackish prefers dodgy or wonky.