The reconnection is faster, but unless you are using 802.1X with a distant (high latency) authentication server AND an extremely time sensitive application (e.g. VOIP), then 802.11r will probably make no noticeable difference. Windows won't use 802.11r unless 802.1X is also being used (no PSK, but per-device or per-user username+password auth instead).
Each wifi client decides when it should roam. Whether it roams more "eagerly" if 802.11r is enabled is completely up to the device (on Android this is decided by the OS, but might be overridden or disabled by the phone manufacturer, on Apple devices this is decided by the operating system, on Windows this is decided by the wifi device driver and each wifi chipset manufacturer has different behaviour). You might get a bigger win by enabling 802.11k (but that is more difficult to mange with OpenWrt at the moment).