"i-Voltmeter" is probably a terrible name for getting the attention of the kind of people who actually want cheap sensors for experimentation, i-Stuff is usually shiny and locked down, whereas this voltmeter is described as Open Source hardware, and really, it's pretty straightforward to talk to bluetooth devices in general, most of them are "serial ports without wires" and that's actually good enough!
On top of that, if you actually make it further down the web page, it becomes a lot clearer that "voltmeter" (or ohmmeter) is actually one of the more flexible sensors you can have, since it can usefully hook up to most environmental sensors (light, temperature, reed switch) with nothing more than alligator clips. It's "good glue" for this kind of thing; it has a different "scaling shape" than things like the Twine box - the Twine can itself hook up to a bunch of sensors and then you talk to it wirelessly, here you can have the sensors themselves farther from a computer (and farther from each other, even outside if needed.)
Unfortunately it's a high-starting-point ($65k) project, apparently because of bluetooth radio certification (compare, though, the Ubertooth One OSHW firmware-replaceable bluetooth security analysis tool only needed $16K to get off the ground, but I'm guessing it's in enough of an "experimental" category that it didn't need as much certification/overhead to get built.
Still, this kickstarter is open until 13 April 2012, so if you're interested in More Cheap Sensors (one of the interesting bottlenecks in household robotics in particular :-) it's worth a look.
update This kickstarter was canceled early, on 2012-04-05.