A plus is an immediate pressure relief once the trigger is released, so you don't get a drip from the end of the tube. You can hear the clutch click just before caulk is expelled, so you know when to start moving the gun.

It's reasonably compact, although it might be a bit tight if you were trying to caulk a toilet base, for example. Just break out the manual gun for that.

It has a variable speed dial on the back, to control the flow rate depending on what you are doing (slow for caulking, fast for adhesives).

It will squeeze every last bit out of a cartridge.

It comes with a trigger lock; witch comes in handy if you have curious/doofus neighbors/brother-in-laws around that want to see how it works, when you aren't looking.

Milwaukee claims you can expel 10 cartridges on a single charge. That may be a bit optimistic, and will depend on the bead size cut into the tube, the viscosity of the material, and even the temperature. However, if you are doing 10 tubes a day or more, just get some extra batteries. It uses the same 2.4 V battery as in Milwaukee's cordless screwdrivers.

Although it isn't listed, it comes with one battery and a 1-hour charger.

I bought mine because I purchased a house where all the windows needed to be caulked, not because I will use it to make a living. I reserved one star because it's a just a little bit pricey (more expensive than the more substantial SawZall, for instance), but you never regret buying a nice tool in the end. It's not out of the question for the typical homeowner who happens to be a bit of a tool freak.

If you are a contractor, you might want to look at the new 12V guns Milwaukee just came out with, but they will certainly be a lot heavier.

It doesn't make caulking fun, but almost.

Review Of Milwaukee MOdel 6550-20 Caulking Gun (Rating: 4.00)
Review : This is a convenient tool to have available when working with 10 oz. cartridges of RTV sealant, molding adhesives, etc. Power comes from a 2.4 volt rechargeable battery. I've discovered that a single charge of the battery is sufficient to use continuosly on 2-3 cartridges but if you stop using the gun for 1-2 hours, say a lunch break, the battery will need to be recharged. It apparently loses it's charging capacity if idle for more than 1-1.5 hours. I therefore, strongly recommend buying a second battery for large jobs. The instruction manual lists a 10 cartridge capacity on a single battery charge but that appears to be overly optimistic. Model 6550-20 is heavier than the common hand operated caulking gun, but the disadvantage of the added weight is overcome by the ease of the trigger mechanism wich easily expels sealant. The caulking gun expels sealant as long as finger pressure is applied to the trigger. The moment you remove pressure on the trigger, the plunger mechanism stops pushing against the cartridge and no additional sealant is expelled. Unlike hand operated caulking guns, I've experience absolutely no excess sealant pouring out once the trigger has been released. There is also a trigger locking feature which allows for continuous operation of expelling sealant. I've found that a two click racheting sound is emitted from the plunger just prior to the sealant being expelled. This sound is caused by the plunger making initial contact with the back end of the cartridge. This racheting sound is convenient since it signals the moment just before the sealant is about to be expelled. There is an adjustable knob on the gun body which adjusts the plunger speed and thus sealant flow. I've found however, that the amount of sealant used is dependent more on how fast one can move the gun along a bathroom tub/tile line than the speed of the adjustment knob. The gun comes with a handle strap, which easily slips over your hand to avoid accidentally dropping the gun. This handle strap is extrememly helpful when using the gun in such awkward places as high up on a ladder. Asided from the limitations of the 2.4 volt battery, my only other complaint regarding this gun is its somewhat large size which is difficult to maneuver in such tight spots as the space around the toilet bowl and nearby walls. Although the price for the gun is prohibitive when compared to a hand operated caulking gun, the investment is well worth the expenditure if you have several bathrooms to caulk. Unlike hand operated caulking guns which require a constant hand applied force to expell the sealant, the model 6550 requires only finger pressure on the trigger and when the trigger lock mechanism is engaged even that is not required. This is a feature your hands will certainly appreciate after using two or more cartridges of sealant.