My experience has been that the closer you are to the stereotypical poly person in your area, the more welcoming and useful the poly groups will be to you. For instance, in my local group, the majority are kinky in various ways, many are pagan, most are geeky in some way (with lots of gamers), and most are straight-ish, lean heterosexual.
I'm geeky, a bi woman (who identified as a lesbian for a long time), fairly kinky, and lean pagan spiritually. So I fit in just fine and have had a positive experience. I've been very open about my dykey past and have experienced no issues. I do wish they were a bit less hetero focused and have been actively encouraging the community to move in that direction. But, and it's a significant 'but', I am not a bi man. There are few openly bi men in my community and I wonder if that is true in the US poly communities in general. Brazil may be very different - I hope so. However, even if you don't fit the profile, be yourself anyway and encourage, perhaps gently, your local community to move towards you rather than the other way around.
And the point that while the poly group may not be your cup of tea, you will likely meet some worthwhile folks anyway, is well taken.