Veho Smartfix 3 Pack of additional scanning slide trays

I had lost my original pieces so could use my slide transfer tool these worked beautifully so have been able to scan over 1500 slides, my only adverse comment would be that the three pieces are exactly the same so not sure why we have to by 3 of the same

When I bought the complete unit years ago it came with 3 different slide holders so that I could use any old slides. This pack is 3 of the same design. Why would you need 3 of the same design? I assumed, wrongly, that I would get the same as the original pack. My mistake, but cannot see the dense of this pack.