Being a dealer with almost nothing but grief from Hesse/Vulcan receiver guns, in almost all cases I would say run for the hills. Only one Hesse firearm I sold did not have problems (it was an STG-58/FAL, rough as a pig but I got it worked over and looking good). The STG-58's were usually 50/50 as to successfull operation. One Garand I had literally disassembled itself though the receiver was pretty to look at. I have seen an AK receiver so warped I can't believe it could leave a factory.
Several have bought the carbon fiber receivers, they seem to be better than his usual crappola. I bought a set of them myself. Of the 4 reports I read, 2 were bad, cracks started to appear. One was used for full auto. I had always planned and still do to use my set in a dedicated .22 rimfire build so stress won't be a big problem.
I will always recommend against Hesse/Vulcan receivers (hell, they are so notorious they had to change their name to Vulcan). If you get one you are rolling the dice, and the dice are usually weighted to crap out. If you gotta go Carbon Fiber, I would highly recommend try Bushmaster instead.