HELP! Where do I start with my new overlocker?

Okay, so I am extremely excited as I just bought myself a new overlocker today. Here it is...

The clever sales lady convinced me to upgrade from the model I was going to purchase which was a 'cheaper', on special one than this one, however this model 'self threads'. Now I am jumping the gun a bit here as I haven't even taken the Overlocker out of the box yet! I have taken the instruction booklet out but I am yet to read it. My neighbour popped around today and said she has the same model Overlocker, however it is a lot, lot older. I found this quite reassuring, because if they have continued to make this same model over the years, you would think it is a good one and in demand, right? My lovely neighbour said it is a solid machine which will last and last. She also gave me a nifty tip on the threading which will save heaps of time and stress!I will post about it later once I have actually used the machine! By then, I should be able to explain it better. The purpose of this post is to generate (hopefully) some discussion about this model Overlocker in particular, but also about overlocking in general. My question is this...when Overlocking fabric that is 100% Cotton, should you always use 100% Cotton thread, or is Polyester Thread okay for overlocking? My preference is to use 100% Cotton thread so that 100% Cotton fabrics do not get 'torn' by polyester thread, however I am a little daunted by the cost factor in purchasing those big thread cones in 100% Cotton. What is everyone's thoughts on this and various experiences? Thanks. x Tanya