Integral strikers are on approx 98% of British boxlocks. Disk set strikers on boxlocks are relatively rare….kinda like intercepting sears.
The 400’s do have disc set strikers, and that’s great…if you have additional strikers already made to fit and, and this a biggie….if you can remove the disk itself. Simply having a tool that fits the disk isn’t enough in most cases, especially if the disk tool is a hand tool like the type you find in gun cases, etc. In my experience, to get the disk out, it is done with a tight fitting, custom made tool that is also fitted into a belly brace or hand impact driver to get the disk to even budge. Many disk are damaged so badly during removal that another must be made and fitted in.
400’s and 700’s suffer from the same flaws. The barrel hook. I don’t think the screw grip bite adds much of anything, probably why they redesigned the gun into the 700 series.
Either one is a proven performer and with proper maintenance and care will last a lifetime or 2.
I do like 400’s for the same reason MC stated, the higher graded guns were wonderful. Beautifully engraved and the fit and finish are usually very nice. I’ve owned a few. Nice guns.

I hope “gunman” comes along shortly, he probably is the most knowledgeable guy on here about mechanics of W&S stuff…..he apprenticed with them.