Unfortunately, in over five decades of acquiring and using detectors, I have made a few mistakes. Sometimes a new acquisition wasn't terribly bad, it just didn't complement my detector outfits. Sometimes the performance afield was a bit lacking, and on one or two selections it seemed a lot just fell way short.
Then, what works for some folks for certain applications, just isn't quite right for others. The DFX is one example, at least for me. I owned 4 of them, thinks that what I had prior just wasn't working right. I had owned a few other SMF's, and I thought the DFX was maybe a step up. For me, it wasn't. I had wonderful success with the XLT's I had owned since '94, but after several in-the-field comparisons done side-by-side on located targets I quickly got rid of the DFX units.
As for SMF detectors, I have owned a few DFX, CZ, Sovereign, Explorer series, Vanquish, Equinox 800 and Garrett SMF Apex models and, today, I only have a few Garrett Apex devices. I like them due to their excellent balance, light weight, and because they did a very good job on their first SMF detector.
Also because they provide the option to select a Single Frequency, which I do use quite often compared with running SMF all the time. In quite a few hunt scenarios, I have done better with a Single Frequency than Multi with both the Equinox 800 and Apex. There are times when a Multi-Frequency function works a bit better, and other times when it falls short of a good Single-Frequency.
Of my 10 detectors, some assigned for Tot-Lots, some for remote site Relic Hunting locations, and some more for urban Coin & Jewelry Hunting. Not all of them are 'modern' like my Apex devices. Some of them are still current production, like the two I just acquired this past week, the Teknetics Patriot and Fisher F-75+ which share search coils, and some are discontinued models that also work great. Those would be a more dated Tesoro Inca, Silver Sabre microMAX and Bandido II microMAX, or my Nokta FORS CoRe and FORS Relic. All of them will have their own strengths and weaknesses, but with the right sets of coils for each, I can pick the combo to serve my needs ... anywhere.
No doubt you'll end up with a few models of your choice and be ready for retirement in the near future. Just take your time, select them well, and maybe part with whatever is useless and simply 'clutter'.
Monte