Got my Ferrous today, and though I only played with it a little while here's my quick review.
It's not a "eBow but better", it's quite a different thing. Where an eBow has a pickup and generates magnetic feedback, this is just magnets on a rotating disc You set the rate of rotation with a dial (and/or a button, inconveniently placed touch plate, or CV input). When you reach a frequency that matches potential modes of vibration, then you get some sound.
Depending on the instrument in question and how you hold things, it might be extremely finnicky about the rate, or it might have a relatively wide range that will excite the string/tine/etc. and bend the pitch if it's not dead on. It might be pretty quiet, or a reasonable volume for a quiet instrument, or it might get pretty noisy.
The magnets are not *super* strong. It can be a little tricky to hold it close enough to work but not scrape the strings or get pulled in by the magnets. There's a little doohickey with a rubber tip you can screw in to one end to help somewhat, without which it'd be much trickier.
The gizmo itself is mostly nice to hold in terms of shape/size, though the edge of the PCB surface isn't a super smooth thing. It came with a 9V rechargeable battery that has a USB micro charging port right on it, which I haven't seen before.
Instrument results:
Miezo: I tried this first before really grasping how the thing works, so I need to try it again later. It can for sure move the strings, but like I said, it's not an improved eBow. So the best bet is to hold it between a couple of open strings and vary the pitch to resonate different strings... not really super exciting. The pickup absolutely grabs the sound of the spinning magnets though so you can "play" that I guess (also not super exciting).
Kalimba: There are lots of tines and they apparently have a lot of vibration modes and the pitches are willing to bend... so it's very eager to sing. In fact if you match the fundamental of a tine too closely it rattles quite loudly -- it takes some finesse to get it to stay clean.
Small cheap steel tongue drum: Pretty meh, I was able to get a very soft major third out of it from two of the tongues but that was about it.
Bowed psaltery: Worked very nicely. The strings were easy to excite but not over-eager and you can get some neat harmonic sweeps etc. by varying the speed.
Dulcimer: since it's tuned D-A-D there wasn't really a lot to work with. I thought about experimenting with other tunings but it's my wife's and I'd better not.
Ibanez Mikro: at this point I was starting to get a better feel for the Ferrous. Not exciting results though to be honest, but I was playing it unplugged.
Acoustic guitar: worked quite well, louder than the psaltery if not quite so rich a tapestry of strings to choose from.
Cheap old electric guitar with bad strings: kind of OK, nothing like the acoustic guitar though.
Mandolin: kind of OK but I'd rate it lower than the guitar and psaltery.
HAPI drum (larger steel tongue/tank drum): I could get one tongue at a time to resonate weakly, just not that exciting.
Remo Ocean Drum: I figured this would either do nothing, or violently rattle the shot inside the drum, with a slight chance of being cool. What it actually did: nothing.
Marching xylophone: nothing, I suspect the bars are aluminum.
Have not yet tried the lap steel, but I feel like it could have potential. Nor the beat-up taishogoto, which I predict would be similar but inferior to the dulcimer.
An autoharp might be ideal and a piano or a Rhodes could be fun...