I have both system: with a single block on the 5.2 and with the back to back pulley on the F16. I prefer the simplicity of the first one as there is no need for a purchase there. I may retrofit the F16.
When retrofitting, does your spi' halyard length need to change?
It may need to be a little longer, depending on the length of the 2:1 system and the distance between the snuffer and the end of the pole. In my case I am lengthening the pole to accommodate my new spi, so I'm going to have to change all of them probably as the distance snuffer/pole-end increases.
Another way to see the needed halyard length is to look at the length of halyard left on the trampoline. With the spi up, there should be no difference between the two system. Bringing the spi down is going to consume some length of halyard to let the pulley travel forward along the pole. The single line system will travel 2 times the way a back-to-back pulley line would do, so it's going to remove from the trampoline an additional pole-end/snuffer length.
Depending on your perspective, the single line system will clean up you trampoline more when you snuff down or the dual pulley system is not going to let as much halyard on your trampoline when the spi is up...
