I have to ask what is polyester mainly used for or why polyester instead of bonded nylon. I'm asking because of curiosity. I just bought a paff 145 h4 and it came with a new spool of polyester.
Try the thread exchange. I myself have never used polyester I have always used bonded nylon. I am a parachute rigger and bonded nylon is what is used in the industry
One other thing is if you don't know what your needs are do not buy a machine o f any kind until you know what you want to sew. I am not saying this to be rude or anything of the kind but trying to help you from making a costly mistake.
You are way way better to not gat any machine until you find one that meets your needs. Save your money until you can buy what you need and not just any sewing machine.
Go to a Head Stone maker and ask for a waste piece. The one I have is 5 inches thick and it is the best for setting stamping or skiving. You can also go to a counter top place and get scrap I have gotten both for free.
I loved the one I got in the 70,s when I first started leather craft but then years ago I found leather wranglers and that is by far the best blade I have ever used.