Yes and no. All depends on the machine and the principle it works on.
P.I. machines years ago drank power so had pounds of batteries and lacked sensitivity. By the time they had become easier to use (motion principle) they were able to provide as much depth off a normal battery pack. Improvements in sensitivity have continued in the last few years. If the detector is P.I. and under five years old then you will have a deep and sensitive machine.
Then you have the likes of the Sovereign. Multifrequency that handles salt conditions really well. There has been slight improvements over the years but I would be happy to use a brand new one or one ten plus years old. The new GT is the best yet but the older machines are only a little behind sensitivity wise. Main improvements were just in adding more external controls. ie flick a switch to turn off TONES. With early models you had to open up the control box and move a small jumper .
With the Excalibur the build quality was a little iffy for many years in a knob falling off kind of way. Last few years production have been far better.
Fisher twin frequency detectors didn't improve much in performance so you could buy old or new but the original CZ6 had a flying lead for the headphones that could give problems and a unique coil connector so if you buy one you can't just stick a new coil on. CZ 7 discharged its batteries whilst not in use. Solution, drop them out but its a pain to have to remember.
Headhunter. New models (under two years ??) have a revised set up on the phones so that they don't turn back on themselves and damage the wiring.
DFX. Don't think any change has been made since it came out.
So you can buy an older machine and save money BUT do check it out if you do. Something off E-Bay might look O.K. but could have been dropped in the sea or have all its switches full of sand or knobs that hardly turn due to corrosion.
A local buy or a trade in that your local dealer has can be checked out. Otherwise you could be buying a lemon.
