I bought some Kevlar thread from Ebay with the intention of making my own Kevlar food bag. The thread sucks. It frays very easily an creates a birds nest in my sewing machine. Waxing the thread may help but who has time for that. If it does tangle in my machine (and it will, believe me)it stops the machine cold. I could see it causing damage to a sewing machine. The thread works better when you are hand sewing, but most of my project are on a scale that hand sewing is not feasible.
The thread by itself is very strong but when you bend or knot the thread it breaks pretty easy.
I do still carry a small spool of the thread in my hiking gear because it's strong enough to be used for many things besides just gear repair.