Is your question about 'plasma balls' rhetorical or are you seeking the answer?
I suppose it could be used as you suggest, but it would be more for show than anything else. The Fingerworks hardware works by measuring capacitance, not the flow of electrons, so it would be different in that respect. I am not sure what you would use to 'count' the flows or otherwise differentiate the flows so you could use it as a 'mouse' but I am certain something could be made to work, probably the biggest issue would be maintaining transparency so the plasma flows would still be the stars of the show, so to speak.
As for RSI, its not why I got into FW, rather the technology is just so absolutely cool. I got into computers via architecture and CAD, so my first 'mouse' was, in fact, a puck on a graphics tablet, which has so much more functionality than a mouse its simply not in the same league. When I subsequently ended up needing mobility and switched to notebooks, the graphics tablet was just too bulky and there were none that worked off of battery or USB (which hadn't yet become pervasive) so it was either learn to use a mouse or learn to use the builtin touchpad, I choose the latter and so have never used a mouse. Touchpads even then had some interesting though extremely limited gesturing capabilities. I would have gotten a TS years ago but for the pricetag. When I built my latest machine a bit over a year ago, I saved so much by building it myself I felt I could splurge and so bought my first TS. If I had known at the time they would cease operations less than a year hence, I would have really splurged and gotten a half dozen or more. Ah, the curse of 20/20 hindsight.
You best bet is to scan EBay (make sure you use Worldwide or Global in advanced settings) and Craigslists (again go for worldwide or global). Keep a watch on the Marketplace forum in here, I make a point of posting every Fingerworks listing I come across so at least people know about them. I am not currently in the market so I am not your competition. I urge everyone else to help out in this. I'd also say that everyone should please maintain a bit of sanity in all this. When the price gets too high, stop pushing it higher. You are doing all of us a disfavor. I know folks want these devices and in some cases will pay whatever, but when its obvious somebody is going to pay whatever, let them have it, another will come along and if they already have theirs, they are not as likely to bid on the next one, unless the prices get so high that speculators get into the act and they will push the prices higher and higher with the sky not being the limit.
Yeah, yeah, I know, its easier to say that when one already has theirs. But one thing is for sure, pushing the prices up helps no one but speculators.
Invent the Future