Size of the tank is fine, but its really about the horsepower of the motor and amount of air motor can put out so that you don't have long period of motor running in order to build a pressure in the tank.
Compact unit, poor packaging - my unit arrived with the plastic air intake filter housing broken. In the mean time I have patched the filter housing back together with electrical tape.

Other than the poor packaging; the unit is easy to operate, stable, compact, and provides plenty of air for general household use. Its duty cycle is limited to 30 minutes per hour, so it is not intended for heavy continuous use.
Heavy Duty versatility - First off I am a homeowner, not a contractor and have been using this compressor in my house to do renovation trim work for over two years.
It is a fantastic compressor for my purposes. I run one in to my garage for airing my tires, and one in the shop for projects.
When I move the compressor in to a room I am renovating, the two outlets also let me have two tools going at the same time, i.
I will tell you it is LOUD but so are all compressors in this class, and this one is not as loud as my last old Campbell-Hausfeld. So if you are planning on moving your compressor around a lot, this is the WRONG compressor for you.
But if you want a relatively stationary compressor with greater than ordinary capabilities, you may agree this is the ticket.
First Impressions... - It only took 3-days for my new compressor to arrive at my doorstep! And best of all, the shipping was free! I immediately unpacked the unit and checked it over. I followed the manufacturer's advice and went through the 15-minute break-in period leaving the tank drain valve open while the motor was running. Although I haven't used my compressor yet, first impressions are everything. This unit is compact, relatively light weight, fairly quiet, and fills up extremely quick! I can't wait to attach my air nailer and get to work!!!.
Darn Good Little Compressor - Short and sweet - this compressor delivers on its promises - it is easy to use, easy to break-in, easy to maintain, and you can't beat the duel air hose inlets. I have found both of the built in pressure gauges to be accurate, and the oil-free motor is quieter than other compressors I have used (although it still makes a good bit of noise). To me, that's portable - I can understand how that would not be the case with everyone, but my experience leads me to believe that this compressor has a very good weight-to-horsepower-to-air storage capacity ratio.
Plenty of Power to Offer...but it needs plenty, too. - I tried the compressor on an
undedicated 15 amp circuit, and it immediately blew the switch every
time. I called Porter Cable and they admitted this 3HP motor NEEDS A
DICATED 15AMP CIRCUIT (with nothing else on the circuit to compete).
I also learned (the hard way, of course) that if you are using the
compressor with a 50' extension chord (with too high a guage) on a 20
amp circuit, the pump will not get enough electricity to pump air
after cutting-in when the tank pressure drops to 110 psi (the
specified cut-in pressure) - the pump will start pumping, but quickly
stop and you'll hear the motor straining until it blows the 20 amp
circuit, too. It's
cheaper, my new Porter Cable friends say, to buy more air hose than
the right gauge extention chord - Ah, such knowledge I'm gaining.
Sadly, the compressor arrived with an air intake filter housing badly
bent downward (done apparently at the factory, as the box from Amazon
wasn't damaged), so I couldn't remove the air filter. AND, the drain
valve (to drain water from the bottom of the tank) would not
completely close allowing lots of air to excape from the tank. In my
chats with an Amazon tool sales rep, and later with a Porter Cable
tech rep (to help me unravel the compressor's electrical-needs
mysteries), both Companies quickly and nicely insisted on sending me a
new air intake filter housing and a new drain valve (I guess I'm
getting two of each?) - no questions asked. The machine is fairly
loud, but it only takes my pump about 6 seconds to refill the tanks
from the 110 psi cut-in pressure to the specified 135 psi cut-out
pressure. I figure the noise level goes hand-in-hand with the added
power this compressor offers - power I think I need.
Excellent compressor - quietest I've used in its category - I am never able to live without a good air compressor. I use them for a variety of tasks from simple blowing to nailers and air hammers. As smaller air compressors go, this one really delivers a nice, steady pressure for quite a long time.

Normally I like to blow through my air gun at about 50psi to clear sawdust. Blowing air at that pressure really drains a small compressor fast, but this one really handles it well and gives me quite a bit of extra time due to the fact that the motor really kicks in quickly and efficiently to keep the pressure up.

I couldn't outpace the compressor with a single nailer.

The two air ports is really nice in one this size because I can put the compressor underneath my workbench and mount a static line on my workbench for easy access anytime while leaving the other open for longer hoses. These size compressors can make an INCREDIBLE amount of noise, but the Porter-Cable 3hp 4 gallon side stack really keeps the noise level at a minimum.

Let’s face it: This compressor’s big, heavy and loud, with a max psi of 150. You can run three or four guns at once off it with a splitter and have no air supply problems whatsoever. It’s built tough for the job site (and the trips to and from), with a full roll cage to shield your pump and motor.5 gallon, oil-free contractor style compressor is packed with features. The high-flow air regulator and two-port removable console are winning combinations for contractors. Having the ability to remove the console gives the user the opportunity to remote air regulation and gain higher air pressure closer to the job site. The full roll cage frame adds protection for the pump and motor. Air delivery at 40 PSI: 7.

What's in the Box
C3151 Job Boss Compressor, mobility kit, manual.5 gallon, oil-free contractor style compressor is packed with features. The High-flo air regulator and 2-port removable console are winning combinations for contractors. Having the ability to remove the console gives the user the opportunity to remote air regulation and gain higher air pressure closer to the job site. The full roll cage frame adds protection for the pump and motor.

Product Description
Includes Compressor, Mobility kit, ASME safety valve, Operating manual, Limited one-year warranty.