I used a fertigation system that I built myself.
The only time I had a problem was when I mixed Calcium Nitrate with just about an other fertiliser.
Calcium does not like staying in solution so you have to put it through separately.
Fertigation is great as long as your irrigation system is built well.
I had an orchard with under tree sprinklers and fertigation was wasteful because I was fertilising a lot of ground in between the trees. This is not so good for small trees not so bad when trees are full grown.
Drip irrigation is great for fertigation The plant roots grow where the water is and the nutrients are delivered right into the root zone.
You could get problems with soil acidification so you need to apply something alkaline every now and then.
If your soil is already alkaline its a bonus.
The problem buying a system from a company is you might be paying too much for your nutrients.
If you have some basic agronomic knowledge and can take some leaf samples from time to time you can work it out yourself.

i had fertileearth profeeder installed last week by my irrigation guy. sorry for lengthy response, but now i know some tricks, so:
1. he messed it up to the point of no operation. so, install DIY; use unions and materials from home depot, my cost was $27 without jumbo valve box. took me about 1.5 hr to undo what the guy did, go to home depot, buy the right parts, and retrofit it in myself. absolutely get sliding adaptor for the main line, made life so much easier!
2. it does work. i paid $139 plus shipping for mine, got it from here:
SmarterYard.com
unit came in about 8 biz days down the road.
make sure that when you install it, after you run water, it starts doing whirrling noise and clicks about every 20-30 seconds.
i am dead DIY person. so, i am not going to pay $40 plus for their fertilizer. their bottle is said to last 2 mths. i went to wallmart and got 4pack of miracle grow liquid fertlizer - $10; i had liquid weed control and insects control on hand.
so, what i did, was that i took enema bag, filled it with mix of all three, and hooked it up to the profeeder unit.
[IMG]http://i37.tinypic.com/2rhtt6q.jpg[/IMG]
[IMG]http://i34.tinypic.com/24fzous.jpg[/IMG]
bag is filled up to the edge to create air tight environment; i put it into unused garden hose holder and covered with insulation to prevent evaporation. bled the system and it's ready to roll.
i am very excited about this. it makes a lot of sense, esp in my case, when soil is very poor and water sifts through very fast. i'll see how goes it, but am sure there will be a lot of difference.

correction to my post from yesterday.
i do not think profeeder will work with drip irrigation.
it is a turbine propelled device, has 2 differnt size nozzles that create more or less jet stream of water on the turbine. drip system have very slow water flow.
matter of fact, zone 9 on my irrigation system is rigged drip system. i asked them to install a garden hose connection there, as i was intending to connect a purchased drip system, just to realize later that it will not quite work for that flower bed. so, i have old garden hose with holes punched in it attached.
i had that zone running yesterday, and, after initial whirl, profeeder stopped working off that zone.
i don't know about EZ-flow one, it might work as it is not "in-line" feeder to my knowledge. but it's just a wild guess, i have no experience with it, just off-line knowledge.