I have used an LVM "Hi-Speed" 12V Inflator/Deflator for 2 years now (LVM make Aerogen and Aquagen generators). It is recognised as the best (and probably most expensive) on the market, very favorably reviewed by magazines and recommended to me by several friends. am completely satisfied - it fills each Avon chamber in about 30 seconds. Deflates to allow VERY compact packing and storage.
Be aware it draws about 20-25 amps (rated at up to 400 watts), and I understand the motor is not "clean" electronically. This means you cannot have long leads unless they are thick enough to carry the amperage the distance, and it is not a good idea to run it off the same batteries as your electronics unless you can ensure they are shut off. I have it "plumbed" into my engine rather than domestic battery, and use it with the engine running just to be safe (a little like an electric windlass, but not so bad). I have a flex lead that I put out through a hatch in order to avoid having such a high amperage socket on deck exposed to weather.
A great little tool - I highly recommend it if you inflate/deflate your dinghy frequently. I reason that it is safer to carry the dinghy on deck at least partially deflated than to tow it. This is so easy with the LVM pump.
My recommendation - if you cannot afford the LVM, don't bother - use a hand pump.
Incidentally, I have an inflatable floor in my dinghy - the LVM does most of it but cannot complete the job perfectly. To get it really hard I still use the high pressure side of the hand pump briefly to finish the job.
Also got an LVM. Inflates/deflates Yamaha 2.6 metre tender and Yamaha 3.1 metre fishing boat in minutes.
Disagree a bit with Edward on battery technique as LVM recommend that you don't have the engine running when you use the machine.
The drain caused by the LVM draws the battery voltage down so much that it results in the alternator boosting the charge to the battery to compensate. The net result is that you finish up with over 12 volts going to the LVM which is bad news for longevity.
On the boat I use the "instruments and domestic" battery with everything else turned off. The whole job takes so little time that even at 25 amps flattening the battery is not really a problem.
Going fishing with the bigger inflatable I use a small motor-bike battery as sometimes it is easier to hump the boat to the water in its two bags than inflate it near the van and then wrestle it to the water's edge.
The LVM has a pressure relief valve that stops you over-pressuring the inflatable. (You know it's opened up as the "tone" changes.) Maybe Edwards has a bit of grit under it as the one I have takes the two boats well into the "hard enough" range.
"Hardening up" floors with a foot pump is not so bad as the floor is kept cool in the water but be careful if you "harden up" the side tubes. Maximum pressure plus a bit of sun = over-pressure fairly quickly.
As Edward says there's no point in getting something that only half does the job so - go for an LVM.