Are there any disadvantages in the portable version? How reliable is it since it's not by the official developers?
It is exactly the same as the normal version, except, of course, it is portable - you can carry it around on a USB stick and use it anywere. I've used it before, and never had any problems with it.
You can even copy your preferences from the normal version into the portable one, if you like.
Hope this helps

Beanie