I have the FORS and had the DEUS. You can find stuff all day long with either detector. So the real question is what kind of detector do you want to find stuff with all day long?
The machines are exact opposites physically. DEUS is half the weight, control box, coils, and headphones are rechargeable, entire system is wireless. You have limited, very expensive coil options with DEUS. FORS is old school, four AA batteries, wired coils, standard headphones. You can get both smaller coils or larger coils than for DEUS at less than half the cost per coil.
If you like having extreme versatility of adjustments the DEUS allows for the selection of many options. These can be saved as programs. One of many things you can customize a lot on the DEUS is tone options. There are preset programs to get you going but learning the machine can take quite a bit of time. A common criticism of the DEUS is it is hard to master.
FORS is very basic, more turn on and go. Most people will either choose from the preset two tone or three tone options, ground balance, and go. A common criticism of the FORS is it is too basic, not enough tone options.
Look very hard at the settings available for both. I highly recommend you download and read the owners manuals for both detectors. It may simply come down to whether the DEUS offers features you want that the FORS lacks. Or it may be FORS has all you need. Do you like lots of options, or basic settings?
For me basic is fine, but mainly I am a fan of small coils and there currently is no small coil option for the DEUS. If there ever is one, it will likely cost over $400. I was out yesterday merrily extracting targets from an area I was over previously with the DEUS. The DEUS 9" coil (254 sq in) simply can't compete with the FORS 4.7" x 5.2" DD coil (77 sq in) in thick trash.