But...
I honestly found that cosmos gave me no extra lag, or spam and if your worried about bugs, I only ran into about 2 a week...not many.

A replacement for reloging-just do /console reloadui does everything a relog does 'cept kick you outa the game for a minute.

Even though cosmos gave no etra lag i decided to look for a different one, and i find taht CTmod is better, just a better setup imo. Cosmos is not for everyone, such as gypsy isn't for everyone, playstyle, i think theres about 3 or 4 major ones:

Gypsy---http://gypsymod.the-mad.net/
Cosmos---http://www.cosmosui.org/
CTmod---(forgot the URL)
Flex Bar---(Never used but it seems a good amount use it)

Go to the UI forums and do a search for em, im sure it wont be hard to find the URL.
WoW Gameplay Discussion -