My 2 cents
I used to sell these HVH spacers and yes the plastic ones did burn up and the aluminum ones were better but I liked the fact that the plastic was used as an isolater but they didn't work for long... I had one customer return his plastic 4 hole that was so warped and disfigured I just was amazed at how it warped and melted... but I sold every one of them.. and the next orders came with DRAG RACE ONLY on the plastic spacers..
I let a Super Stocker buddy of mine try it ( HVH 4 hole aluminum x 1" spacer ) now his race car ran 9.72 with a open hole 1" spacer so he swapped it for the HVH and NO other changes to the car & it ran 9.60 .. believe it or not..that's a lot more than 15 + horse power gain on a 9 sec car..
I sold another one to a Super stocker buddy of mine and he gained 2 tenths on his 10 second camaro.. I currently have one of these on BBC 69 Camaro and believe me when I say these spacers are WELL worth the $100. to buy them.. my opinion only I don't sell them any longer but I do run a 2 hole spacer plate x 1 inch on my other car with a dual plane intake and it runs great, not a drag car..