This is a very handy blower, and very powerful.
One of these is an absolute must for the serious digital photographer using an SLR. The large bulb allows a powerful but controlled puff of air to be directed onto the sensor for regular cleaning in the field.
Also very useful for film cameras, in the camera workshop, and darkroom, and on scanners.
I use one all the time, both in the field and in the workshop to clear dust etc' from lenses, mirrors, and digital sensors.
(You can use a can of compressd air for this, but these are bulky and at several pounds a go get quite expensive. In addition they are a bit too powerful. All it takes is a bit of grit in the delivery tube, and you risk scratching the sensor permanently!)
In the workshop it is very useful for dusting the inside of cameras, and as it is more gentle than a comressed air tank there is much less chance of damage.
If you are still a fan of film, these are very useful in the darkroom too. There is a good handful of air blown out on every squeeze, and this is ideal for negative dusting. I also use mine for cleaning the platten on my hi-resolution scanner. (It's A4+ so it needs quite a big puff to remove the dust!)
The blower has four 'fins' which allow it to stand upright. There are holes moulded into these for hanging the blower on a lanyard or similar so it does not get lost. It is made of soft rubber and is easily stuffed into the corner of a kit bag or a pocket for easy access. (See below!)
Even if you do drop it, it is usally easy to find. The bright red nozzle is easy to spot in grass, or on a muddy footpath. I used to stuff mine in my pocket for easy access, and after the third time of retracing my steps to find it, I decided that a bit of string looped thru my belt was a good idea!
You will see many blowers similar to this described as having a non-return valve. I have checked these out, and the non-return valve thing is simply untrue on all I have tested. You can remove the rubber plug from the 'engine' end and use your thumb as a valve if you like, but I don't see the beneifit. (They are not silicone rubber either! All the one's I have tested are natural rubber, and that is more durable. It's just a softer mix than most people expect.)
The spout is removable, which is handy for storage, and cleaning if it does collect too much dust, also you can remove the plug at the fin end so you can flush it through. (Make sure it is properly dry before using it though. You really don't want to spray water on your sensor!)