Greetings
Feather SE blades will fit
most but not all Valet Razors, there are very many models of autostrop probably at least thirty and the models with the hinged gate that open to one side for the fitting of the blade vary as to where the pins/cutouts are positioned I personally have three of this model with the cutouts in different positions and one of them will not take a Feather blade.
I have also seem another model that will not take the Feather blade that is different from mine.
There is just no way of knowing without trying the blade.
The models that do not have hinged gates or side hinges ie those models where the blade slides in the blade holder from the side will all take Feather blades. These types will also take the modified GEM blades ie GEM blades with the spine removed and a piece snapped of the back at each corner
In short if you buy or are thinking of buying a Valet Autostrop there is a good chance the Feather blade will fit but you need to try it before you know!
I have several original Valet Blades they are IMHO useless, they need stopping before first use (according to the old company literature) and my personal success rate at so doing is 0%. I suspect most of the old strops are knackered and you will need to remove and replace the old loop on the top, every one of mine had rotted and then broke when I used it. My personal advice is that it's the Feather blade or nothing with the model you have.
Feather SE blades are superb shavers but are very short lived, I mean very short ie two shaves and they are quite expensive! IMHO Valet Autostrops are great shaving razors and dirt cheap on e-bay.
This is the best site for seeing the different models:
http://www.stropper.com/home/stropper_index.php?category=
Regards
Dick