They work great, IF you have stock that is planed to an exact thickness and you have set-up blocks. I was super frustrated with mine until I bought the set-up block from Eagle America, worked well after that. But, it's still one of the more time consuming bits to set up, and you will need to make some test cuts to get it dialed.
Having a router lift, or a base that is adjustable from above the table (my Bosch's base is above table adjustable) comes in VERY handy, as you will likely need to make a few very small adjustments to get it just right.
I have one for 3/4' stock, and really, really wish I had more, but being poor, it's not going to happen soon. They do make for really strong joints, though you will need to be patient and take the time to get it right.
I've resorted to splining most times now, as I made a nice splining sled and it will work with any thickness stock, not just one size.