The adapter is very basic since it only uses power parts of 3-pin fan connector. That means if you use the adapter with the fan, then the fan runs with very high RPM all the time and causes lots of noise which is not nice.
I just want to say that case manufacturers should drop adapters like that ASAP. Or at least give users/customers some warnings about it.
It takes only few people to complain that fan in your case is causing a ruckus, and after those complains some people will think that you are providing the cheapeast possible fans for the case buyers (aka customers).
And most motherboards should have at least one SYS_FAN connector. And if you really need multiple fans for ITX case then you can always buy a fan speed controller.