I would imagine its a bit "wibbly wobbly" if your passenger is heavyish? but I suppose these rear saddles were only supposed to be used on a rare occasions.
I can assure you that the four spring versions are not DIY conversions as Globe Motorcycles in Smethwick used to sell them along with other wd types of pillion seat in the 1970s for 21/- shillings which is £1.05 today. I bought 6 pillion seats from Globe which I still have including the the 4 spring version.
