A) The Deben Mk1 and Mk3 do exactly the same job of locating a ferret if used correctly. Sadly, the old Mk1 ferret finder is no longer in production due to the now outdated technology that was used in its assembly. Like so many other things in fieldsports, tradition plays a large part in the equipment used. The Mk3 uses the most recent technology and therefore it can be readily repaired if anything does go wrong, unlike the earlier Mk1 model.
However, special care must be taken to use the right type of collar for the receiver and the correct batteries with the set.
The Mk1 receiver will pick up a Mk1, Mk3 and Mk3M collar, but the Mk3 receiver will only detect the Mk3 and Mk3M collar. Many people now sell the Mk1 finder on the auction sites in order to update to the Mk3 version