Hi @Itaipuaçukites I have the 5m flux, I've only had a chance to fly it a couple times, but it's a very good kite for the $$. Having said that, if you take it out into 30mph winds, you will hurt yourself. I got the 5m to use in 8-18mph. Joel is exactly right with his scale - get either the 3m or 4m depending on your weight and local wind. If you go with a depower, you will probably want something in the 6-8m range to start with. Look up rtz on Randy's link above, he has a review I think on his flux experiences.
Most kite companies (other than Pansh) give you a wind range for their kite sizes. Below are the ranges for a twister, should be somewhat similar to the Flux.
Here's a good explainer for noobs: http://www.powerkiteforum.com/viewthread.php?tid=1985
If you give the folks here some details about where exactly you will fly, wind conditions, how much you weigh they can help you a lot more.