as always its your choice, you can gamble, and I'll stick with best known practice. JD belts don't really cost any extra over other ones, so why take a chance with failure? to me its not worth having a 1/2 mowed lawn or working in the snow to save a couple dollars. I'd run disposable craftsman stuff if I was that cheap.
here is the easy thought to understand. JD pulleys and belts were engineered and tested to work together for maximum performance. the same cannot be said for any aftermarket part, period.
Seeing how well these tractors work after 40 years in service I trust the JD engineers, and in my life I have seen more then enough home grown solutions that 'should work' but don't work right. to avoid having another, if I can get the right parts. that's how I get most of my tractors, one solution after another the was 'good enough' until the PO hated the machine because nothing works the way it should. If I get one with aftermarket belts, they are always replaced asap.