According to VLTOR the VLTOR A5 buffers can only be used with VLTOR A5 buffer assembly components. So it will most likely not work with the Geissele Rifle Length Spring, 42 in. However, I recommend contacting VLTOR to confirm.
This spring will work with the A5 buffers in an A5 length buffer tube. This spring is mildly stiffer than the vltor spring and the Sprinco green spring.
Yes it works, i use this exact setup.