I use a Carry Freedom Y-frame trailer and love it.
I use the small one which carries up to 45KG, although I only carry about 18 KG (for a 2 week camping tour) in the form of a Mountain Equipment holdall held on with a couple of bungee ropes. I bought it because I didn't want to pod out £1000+ for a half decent tourer and so I could use it with my lightweight audax bike. You can use it on virtually any bike - even Bradley wiggins could use it on his racingbike
I've done three 2-week camping tours and never had any problems - it's solid, well made, really stable (even at 50MPH on an Alpine descent), never feels like it might jack knife, and the bike feels and handles like normal, except you have to push a bit harder on the pedals.
The coupling onto the bike is via a nylon coupling onto a metal pin. I use a MTB skewer (which is longer) on my road bike to allow for the coupling bracket thickness (about 8mm). It's never come close to tipping over whilst being towed - it's only tipped over on me when I was pushing my bike down a high kerb, but this wasn't a problem as the coupling is incredibly elastic/flexible and zero damage was done.
The only thing I'm going to change for future tours are my bike tyres (as I currently use totally unsuitable lightweight Schwalbe Blizzard Sport 700x23C, but only because I couldn't be bothered to put on something more durable) as a couple of weeks using the trailer wears out my back tyre. Even though there's very little dead weight from the trailer acting on the bike, there are some dynamic forces which scrub the tyre.
I have used panniers in the past and would never go back to them unless forced to. Therefore I would highly recommended using this trailer.