FS Global is my preferred weather utility, although I keep FS Meteo as a standby as (being a pessimist) I cater for the fact that no web server is ever 100% reliable. It is discreet, reliable, and reasonably subtle with FS2004's weather area changes. When started, it will reload AI traffic to make sure everything is using the correct runways.
As for size, mine occupies 36.3 MB but allowance should be made for the installation process using more than that. However, if you have that little spare space on disc you are running at a high risk of issues generally anyway. You can install FS Global anywhere you like, even on another drive.
All weather programmes are limited to certain quirks of Flight Simulator such as the rain above cloud level. They are also all greatly enhanced with the use of high quality "3-D" clouds, if your setup can handle them.
Hope that helps,
John