I researched all of the Incra jigs as I liked the fact that it could be used on the router table.
I settled on the 17" LS Super System which I've ordered from the states. This includes the Wonder Fence which itself is micro adjustable.
However, I purchased a new Ultra Lite of ebay as I'm still waiting for delivery of my main system. Am I impressed? Definitely. One of the biggest advantages that I can see to the system is the fact that you can swap the system between different machines in your workshop.
For example, you can use it on your table saw to give you a highly accurate fence, you can use it on your drill press for accurate drilling as well as your router table.
I agree, you need a bigger router table but you could always add an extension if you didn't want to go to the trouble of building a new router table.
One of the best sites I found to explain and demonstrate practical use of the Incra Jig was
http://www.woodshopdemos.com/menu2.htm
I looked at the Rat but was put off by the fact you needed a wall which in my small workshop (AKA Shed) was not practical - plus the cost of the thing. My sister went the Leigh route and whilst I was impressed, straight out of the box as it were, I got better results cutting DT on the Incra PLUS you don't have to spend another arm and a leg to get the Box Jointing template.
The Incra is very well engineered and I think is really good value for money when compared to most of the other "professional" type jigs - I discount all the cheapy HBDT jigs you can buy - I have a Perform Yellow Devil which is used as a doorstop now.
As regards what my main use for it will be, initially, I want to get into box making using both DT and box Joints, I like the way Incra do their wooden hinges as well and yes, I was in part seduced by the fancy dovetails which I intend to have a got at when I get the time.
Not a review but just some thoughts on the Incra which I hope some find useful.
Col