I have an Incra Ultra 16 and Wonderfence combination that I use on my router table. I also have a Woodpecker plungelift in the table.
The combination of these things gives me a veritable milling machine that really is accurate to 1 thou.
I mainly use the Incra for its precise positioning, not for dovetails for which I prefer the Rat or the Leigh jig for bigger workpieces. With the Incra I can make the best tenons of any method I have tried and very quickly too. It is terrific for sliding dovetails, again because it can be adjusted so accurately and repeatably. It is quite nice for little box joints but again for anything larger, I would use something else and my Rat is on the whole much more useful for these than the Incra.
With the Wonderfence (a split fence) it is easy to joint an edge if you wish by offsetting the fence but I do all my edge jointing with a handplane as it is so much quicker than anything else.
So to summarise:-
I have the Incra, the Rat and the Leigh, they all have their strengths and weaknesses. Don't buy the Incra for dovetailing or box joints - the Rat is more versatile and quicker. Don't buy the Incra if you want to joint big bits of timber (I use the Leigh for dovetailing carcases).
Do buy the Incra if you need precise, repeatable positioning of the fence (and who doesn't??). Because I use my router table a heck of a lot, the Incra gets most use in my shop compared to the Rat or the Leigh but I would not like to be without the other tools.
Is you table homemade - if not what did you go for? I'm tempted by one of the Incra fences - but have never been happy with my homemade table top - also get a small amt of sag - whatever I do (35mm laminated MDF - but with a heavy Elu 1/2 router hanging from it)! So wouldn't want to spend big money on a flash fence until I had that sorted.
I combined about three different designs I had seen to make it. The top is two layers of 19mm MDF with a decamil laminate on top and bottom. It is edged with one inch oak. It has the plungelift, the Incra and can be fitted for horizontal routing though I use that very little in fact.
If I built it again, I would put storage underneath - the present design is all dust collection - a real waste of space.