I have had V3i and still own 2 complete Deus units.
Differences
Weight,,,big time.
V3i is a boat anchor weight detector that balances poorly with stock 10 DD coil attached-- coil mounts too far back IMO.
V3i is a battery hog,,,get ready to buy rnb battery if you use a lot.
Screen is plum beautiful,,,little glare,,,op can have different color scheme background to suit their eyes and lighting conditions.
Navigation takes some time,,,and their are a lot of settings,,,with minutes changes available.
Learning curve,,I rate as moderate to difficult depending on your experience,,,coming off of DFX will help.
External speaker works well,,good and clear.
Nice pinpoint button trigger.
Deus
Light weight
Charge up batteries and hunt all day
Smaller screen,,,but very legible
Menus are set up nice,,,and settings changes can be made on the fly,,,reground balancing doesn't seem necessary,,,unlike the V3i depending on what you change----- for peak or near peak performance.
Speed,,in separation,,,,IMO Deus with 11" coil outperforms V3i with 10dd coil.
Pluses for V3i,,,modern junk targets if not too deep can be ID by dominant freq displayed on meter,,,Deus can't do.
Depth-- I rate very near one another,,,but there are coil size differences.
Tones
Deus is more digital sounding,,,White's more boxy sounding.
Discrimination system,,,I rate Deus tops here,,,and this goes for more than even the V3i,,,,with the Deus minute adjustable disc,,,you can really pound the iron sites,,,and knock out just the smallest of iron.
All metal,,,,V3i best Deus here,,,Deus AM mode,,,,hard to keep tuned.
Warranty--Deus 5 years
V3i less
Seems both have been receiving good manufacturer support.
Coil availability--- V3i has more different sizes available vs Deus-- currently only 3 sizes available,,smallest is 9".
Also,since the original post in this thread,,,Deus has had version updates,,adding a few capabilities,,,,using full tones is one of them,,,and this feature really makes the Deus what it is-- great Hunter in and around iron.
For deep turf coin hunting,,,where digging is limited,,V3i I give the nod.
For relic hunting,,,Deus wins by a mile.
I hope this helps folks who are trying to decide between the 2.