I don't use any after market "helper springs", but if I had to choose today, I would get the Timbrens. Cheap, light weight, easy to install, not much chance of them springing a leak!!

http://www.timbren.com/

I have the Firestone Airbags. No compressor. I check the air pressure 4-5 times  a year and they stay inflated and do just fine. They have been on my truck more than 4 years. No leaks or problems. Air bags with no comrpessor will be $270-$290 for parts only.  It takes an hour to install. 

I leave mine set at 20 psi for my gooseneck.  If I load up a heavy bumper pull, I might bump the pressure up another 10psi for that load.

The compressors are nice, but not neccessary.  When I sold my trailer,. the fellow that bought it, backed up to the hitch, using a camera with a dash monitor, once the ball was under the hitch, he used his compressor to inflate his air bags and lift the ball into the hitch and take the weight off the jack stand.  Got out of the truck and put the jack away, closed the coupler, hooked up the chains and drove off. I was impressed but not enough to spend the money an on board compressor cost.

The truck I put them on is also our family vehicle (01' F350 CC SRW SB) We like them because they also change the ride with no trailer. I let air out to about 15# last October after last trailer pull and haven't touched them since. They've been on the truck for almost three years in the worst of Minnesota weather with no problems.

I don't know what truck you are putting them on,  I have a 2006 F350 with the B&W Turnover and my Firestone Air bags went in just fine.  It's been four years since I installed them, if I remember right there were two models of bags, one for trucks with out the B&W and one for trucks with the B&W.   Just buy the right model and you shouldn't have to modify anything .  At least on the Fords.

I did install them myself.   It took 60-90 minutes to do.  They pretty much bolt on, No special skills necessary.  I did have to drill two holes in my bumper where I mounted the air valves by my license plate.

I ordered them from some place online.  Just google Firestone Airbags and you'll get lots of places that sell them.   Prices will run from $275- $300  for the airbags.

I've had air bags on several trucks. Never had the Timbrens. Heard good things about them though. The only issue I ever had on airbags was at the fill valve. The inside of the stem started leaking. Replaced it and had no more problems. They are really pretty straightforward and simple.

i have the airlift in mine, control both bags from inside the truck. company stands behind their product faithfully. chevy garage punctured one of the bags and airlift replaced the bag, never cost me a cent. by the way i reminded the chevy garage to not lift the truck by the frame 3times when making the inital appt.

when i went to the airlift dealer he told me he had been a dealer for 10 years, only had problems with one system in all that time.

just thought i would add my opinion.