When it comes to sensor cleaning, you do the cheap and easy thing first. An air blower is inexpensive, easy to use and is the method that you are least likely to damage your sensor with. That said, it isn't foolproof. Air blowers don't remove oil spots and have difficulty removing stubborn particles that stick to the glass surface because of electrostatic charge. Eventually, particles and debris accumulate to the point where a physical contact approach, like wet cleaning, is required. This is where the Firefly Digital Sensor Cleaner comes in; its unique selling proposition is that it has the easy of an air blower, but with better cleaning power. It works, but there are some caveats.
The key to the Firefly's operation is the electrostatic charge-creation device mounted to the front of the blower. In theory, the volume of air in the front unit is exposed to a corona discharge field, creating charged ions that can neutralize the electrostatic attraction between a stubborn dust particle and the surface of the sensor. The promotional literature that describes how this works is a bit of a headscratcher:
"The FireFly utilizes a nine-volt battery to 'ionize' the air passing through the body of the Firefly, producing and delivering both positive (+) and negative (-) air ions to the outlet air stream. This assures that the static charges are neutralized, allowing the particulate matter to be blown off by the ionized air stream and flushed out of the camera body."
The puzzling thing is that if negative and positive ions are being produced, why don't they neutralize themselves before ever leaving the blower? That seems to be the question on everybody who reads into the literature, and to be honest, NRD (the manufacturer) doesn't provide a clear answer. The company doesn't provide any in-depth literature on how long it takes for the charged air to neutralize. The folks over at Cleaning Digital Cameras have done a comparative test with the Firefly. Under test conditions, the device does appear to be effective at neutralizing positively charged surfaces; however, their test description does not include effectiveness with a negatively charged surface. Here is the company video about operating the firefly:
So how does it work in real-life? That answer is that, unfortunately, it is good enough just to be impractical. It most definitely does remove more dust than a conventional air blower. The problem is that even if you discount things that it can't remove, like oil spots, it isn't 100% effective at removing particulate matter. What this means is that even though it is more effective than the cheapest and easiest way to clean your sensor, you will still need to resort to a contact method like wet cleaning in the end. At a selling price of $130 USD, that makes it hard to fit into a photographer's cleaning regime. It doesn't make sense to buy a blower, the Firefly and a wet cleaning kit when you will get the same results as with just the blower and wet clean. Sure, the Firefly might hold off the need for a wet clean, but it's not a cost effective way to to so. In comparison, you might be able to afford 2-3 wet cleanings from your local service providers for the cost of the Firefly.
Are there instances where the Firefly makes sense? It's not cost effective for the solo camera owner, but if you have multiple bodies that see regular use (e.g., wedding and event shooters), then the Firefly makes more sense. Delaying a wet cleaning on one camera isn't much of a time savings, but the economics become a little more favourable when you multiply that by a number of additional cameras.