Have used Anfibio Multi's and Nox 800's, quite extensively, on land and in water. It's been like ongoing trials for me, trying to sort out which suits my needs the best. A couple times now, I've switched from one or the other over the past few years (since nox's came out). They both have there goods and "bads". I finally sold my nox's again and opted for anfibio multi's for one reason or another. The anfibios are heavier, but they are a very well balanced "heavy" with a truly awesome shaft that is bombproof, ultra fast to adjust or collapse, with zero need for any changes or mods. Nox shafts are really junk, old style, sand freezes them up, hassle to collapse, odd "feel" when handling/detecting, they are light and you get used to the odd feel after a bit, just not as nice as anfibio, imo. You can literally run either, with no coil covers and grind them over sand, gravel and rocks with ZERO concern for issues, the epoxy in them are tough stuff and can easily be supplemented with new if ever needed. After countless hundreds of hours, running over anything and everything, i've never really needed to supplement (*i discovered the epoxy minelab uses to fill their coils, can get on amazon, it's like 9500psi strength stuff).
Nox's will almost always be more "quiet" to hunt with, even at highest sens levels, Anfibio's tend to be more sparky/zingy and can be moody when a storm front is coming in with humidity in the air. I've also been in high emi places that drive a nox cuckoo and they are unusable in multi freq mode, requiring use in a single freq.
Both can do ok in heavy black sands, I hunt a few beach spots having massive amounts, it does effect depth some, you can experiment using the different modes on anfibio, like gen mode or try the gold prospect mode of nox to maybe counter the effects. Maybe it's a pi you need for there.
I feel that I can "call" targets better with anfibios and have much more confidence in predetermining junk vs good targets. Also, it's easier to tell the size and depth of targets. With nox's, it seems to "think" a lil too much, often making trash sound superb, which equates to lots of trash sounding good, which essentially means dig everything, to a point. Nox's definitely vdi deeper with the multi-iq thing, but i still prefer using the sounds/clues of the anfibio to determine this. Almost always, with anfibio, if deep old crusty iron sounds good one way, sweep at 90 degrees, if it sounds off as iron, it's like 99% chance it's iron, which has proven very reliable after digging to check countless times.
Both can be effected by cell phone if your phones wifi hotspot is on or sometimes when phone is communicating or whatever with towers.
Battery life of anfibio is excellent, headphones are feather light and definitely higher quality vs the nox ones.
Reach out and see if anyone in the area has either to try maybe. Both machines have surprised me in certain scenarios, both good and bad.
Just some of my experiences/opinions/ramblings, best of luck