I'll give you a newbie's viewpoint. I bought a 2009 AI w/ single trailer late last summer and have gone out in it a whopping 8 times.
The trailer is actually made by Trailex I believe (though, strangely, I don't see the base model advertised on their website right now - their smaller trailers seem to have vanished). Not sure who makes the custom saddles (the only AI-specific parts).
Small trailex trailers are pretty minimalist, just custom aluminum extrusions bolted together, meant for easy shipping. I have nothing bad to say about the basic structure, which in the single's case amounts to an aluminum stick with wheels. This makes it very lightweight and easy to maneuver, so that's a plus in my book. One man can move it around with only minimal grunting. Actually, I started out using it as a beach dolly, hand pushing it across a 30ft. beach. I don't really recommend this though - wheels need to be wider to handle soft sand. Now I launch from boat ramp. It backs up like any small trailer - which is to say poorly - but fixing a jam-up is as simple as getting out and lifting the rear end up and pointing it in the correct direction. Gotta love aluminum trailers.
The one suspect item on the trailer is the "suspension," which is comprised of pieces of rubber sheet clamped between the axle structure and the main beam structure. I know that rubber is used extensively in small trailer suspensions, but I wonder about this particular design (though I've had no problems with it). I suspect that the tires are the most important part of the suspension. Tellingly, they are inflated to a very low pressure (15lbs? can't remember).
The taillights strike me as cheap-but-serviceable. It's not clear to me if they are meant to be submersed, but I'm treating them that way, and so far so good.
Actually, my only real complaint about the trailer is that I think that the license plate mount is too low. I put a 90degree bend in my plate the first time I launched from a ramp (admittedly, this maky reflect more on the primitive ramp I use). I've since mounted the plate higher up, on the rear cross-beam.
Assembly is just a bit annoying. If you do it yourself, set aside a whole day. It was the first one my dealer had assembled and there were some teething pains (make sure the nuts compressing the rubber bits are tight, for instance). Most of the pain is in the wiring phase, which is probably true of most trailers. Trailex still has the instructions on their site:
http://www.trailex.com/Instructional%20 ... ctions.pdfAll that said, I can't imagine NOT having a trailer. I put in by myself for the most part, and I absolutely love the convenience.