Top tip for anyone interested in the Asssaver, that uses the saddle rails, don't be tempted by the copies that ebay is full of , that cost peanuts. They typically have a bike shop name on them, or something goofy, with promises of recyclability etc.
They look pretty much like the short and narrow original, but are made of a plastic that tears/snaps really easily, at a fold line, just aft of the saddle. The material is too much on the brittle side and the fold line is so deep, at that point, the material is super thin.
I got one to see what they were like, compared to a real Assaver, and i clipped it throwing my leg over the saddle, on my 3rd ride with it , and it snapped at that point. I think it was £3.99 or something like that and didn't even last a week!!
My real Asssaver is floppy enough that it bends if you bump it , but holds its shape otherwise. The Asssaver i have had for a while now has a half moon shaped bit that folds up , at the front of the rails , and makes tor a very secure fitting. Iirc the early ones did not have that and just relied on the cutouts for the rails, to hold it in place.
Another thing; i had an early original Asssaver , a while back, and it was clearly made of a plastic that hardens with age/sun. I got it second hand, so i don't know how old it was already, but after a year or two with me it had become very brittle and one day it shattered into 3-4 pieces when i knocked it pretty hard. I think the newest versions have got everything just right.
The not so great copies are good for one thing though. If you use a saddle with an enormous cut out they are perfect , for mounting under the saddle and shielding the cut out, for stopping road spray from soaking your short padding betwixt ball and aerosol. Personally; i don't like that especially with a draft.
Just cut the useless end off , that sticks out from the saddle, and you will have drier padding without the guard upsetting the style police.