The Viking MegaQuilter 18.8 and the Pfaff GrandQuilter 18.8 are both built by Tin Lizzie are similar to their Tin Lizzie 18LS.
If you purchase the Qbot, make certain the Qbot is version 2.07 or 2.09. If not, you'll want to get it upgraded. The upgrade now costs $149, if memory serves me correctly. You will need the 2.09 version, only if your frame is longer than 10'.
Then you will definitely want the 4D Quilt Design Creator software and not the older 4D Qbot Design software. Another $175 upgrade, again if memory serves me correctly. Do not purchase Qbot software, which has already been opened and registered. You wil not be able to transfer the registration. You'll use this software to create your own designs compatible with the Qbot. You can also use any graphics drawing software, like Corel Draw to make your own designs. But the 4D Quilt Design Creator software has some nice features, like background fills.
I have used my Qbot quite a bit with my Pfaff GrandQuilter 9" machine and it works very nicely. I have just recently purchased a used Tin Lizzie 18 and plan to move the Qbot to this machine/frame this weekend.