Just will give ya my a quick 2 cents--
They are all the same inside, Circ, sullivans, Blue Ribbon, and probably some more--- all get the same motors and turbins from the same manufacture and install in thier own housing. Long story short -- price, switches, filters, cords, housings and freight, are basically going to be the difference between new blowers.
I have a couple of older circ II that will run side by side with my brothers new sullivans and cant tell the difference.
And yes - if ya need to replace a motor and turbine, ya can get them from valley vet, sull, or circ, and will get the same identical part. Can also put circ II motors and turbines in the old circ and have the same as a circ II, Circ will tell ya that they used a heavier cord in the circ II.
I have seen several cases where people thought their blower was going bad and found the cord a or plug in was bad and really brought the blower back to life with getting power back to it.
Hope this helps
Have a good one