I can buy either,so what are the difference's between them? Also,any users?(seems the gas guns I dealt with start acting up as soon as the carbon builds up on the mag tube1)

I recently bought a Beretta Urika II semi-auto. The Beretta Urika (with no II) was also available at the same time. According to the literature the Urika II's gas system is "self-cleaning". Possibly the same applies to the Extrema and Extrema II?

I own the extreme 2 with kick off. My brother owns the regular extreme. I used both last fall. I prefer mine. The primary diffference is fit. Try them both. The extreme 2 fits me better because it has a smaller fore end and wrist area. As far as the gas system I have not had a touch of trouble and know of nobody who has. The kick off makes shooting 3.5s a breeze.