I've never used obfuscator in production, but I've tested JavaScript Utility and it seems pretty good.
As for the performance, obfuscated code must be unpacked on the fly each time the page is loaded. Might not be a problem for small scripts, but the unpacking time will be significant with bigger files. On the other hand, minified code is directly executable by the browser.
Some obfuscators might produce output that does not run in older or less common browsers. You should test very carefully with the browsers you plan to support.
