Earlier quoted context omitted.
I'm not an ME or anything, but it would seem washers attest to pressure (tension) at some point in time (when the nut was tightened -unless the washer is "springy", which I doubt as it seems it simply yields at some point), whereas smartbolts attest to the tension when you look at them --so during maintenance and not only during installation, so from that PoV, they are more useful (informative).
That’s true, but you can have a qualified inspector mark bolts with goo with a paint line that straddles to the fastening surface. Then you can just inspect the paint line for movement, which gets you most of the same functionality at significantly lower cost. Of course, that requires a trustworthy inspector, which is one application where smartbolts become useful, if you don’t have a trustworthy inspector available…
What I find somewhat surprising is that they make the "ok" indication black. The cry for attention state in red seems nicely intuitive at first glance, but given the market they serve they should be far more concerned with false negatives than with false positives and I imagine that it would be very easy for dirt or bad lighting to make a red indicator remain unnoticed in an inspection. Perhaps the color choice is an inherent property of the chemistry involved?