Sorry, I have no experience with the Moiss Humidity Controller, neither have I seen it in SG
It looks like a good concept though — can control humidity without a case. Not sure what would happen to the fingerboard though.
I have bought Humidisorb packets which have the same purpose (except the indicating function). They're $18 at Bernard Godfrey Guitars, or $12.50 if you get them direct from the industrial supplier here.
Other similar products would be Zorb-it (out of production) and the Humidipak (from Planetwaves, advertised to last 2-3 months) City Music sells a silica gel pack (with built in recharging function) as well, not sure about the price.
For the indicator, perhaps something more accurate would be the digital hygrometers (can purchase as cheap as $2-3 on ezbuy)
Hope this helps