I just purchased the 700 XL last week and got to making some chairs today.
Let me tell you, it's amazing. I used two 10x80mm dominos in each joint and it worked like a dream. I'm using a hybrid solution with joinery with this chair. For the main joints where the chair seat meets the back chair legs, I'm hand cutting a mortise and tenon joint, and going to pin it as well (where almost all of the pressure is going to be.) The rest of the joints are dual 10x80mms. It takes me the same time to cut two M&T joints as it does to finish all the rest of the joinery in the chairs.
After the Domino 700, systainer, taxes, the Canadian Lee Valley took over $2800 CAN from me. A big bullet to bite, but nothing I can't afford... just hurts. But after using it for this project - I can truly say - The tool is absolutely amazing. It takes a lot of time and is just a treat to use.
It's totally worth the pricetag, if:
1. you can afford it which saves time as a hobbiest and is just a treat to use.
or
2. you are in business
If you aren't making 8 dining room chairs with over 80 M&T joints in total, then maybe you can get away with continuing to cut them the old way... but this will save tons of time.