The main difference between Smith frames and ordinary B.S. frames is that the lugs are shortened to 19 mm giving an overall top bar length of 394 mm.
The other difference is that the lugs are too short for any but self spacing methods.
They find much favour in Scotland, but are not much used in the rest of the UK. I personally have never used them, but I can see that they would be convenient for migratory heather honey production in Scotland.
One feature that has cropped up many times in conversation and Email discussions is the fact that the "Smith" frames will fit comfortably crossways on Langstroth hives.
A serious consideration should be given by hobby beekeepersto the fact that, if they use this type of frame they lose a certain amount of interchangeability with neighbors equipment and if they need to utilise "a frame with eggs" from a friend, then they may have difficulty sawing off the lugs to a shorter length whilst the frame is occupied.