I've not used that brand but have used other conductive inks in the past with good results. One instance was a broken track on a video card where a friend used a screwdriver to push the locking tab and scored the back of the PCB, conductive ink allowed me to bridge the gap and put the card back into service for many years. I would say it has its limitations, probably has higher resistance than a PCB track, and undoubtedly would have a current carrying limitation too so may not work for everything. Having said that you can buy similar stuff for repairing the heater elements found on the rear window of cars.
Basically i wouldn't be making a circuit out of it, or using it replace solder, but could be handy to have for repair jobs.