Unless they are awful they are a poor payback.
HDepot carries a window that is less expensive than the two that you mentioned; it runs about 135 or 125 per window without any extras like the inert gases or appliques for R-values excetera.
What you can do is look at your windows & where they’re facing. If they’re not in direct sunlight during the midday or they have awnings or there on the side where the sun rises and it’s cooler during the morning hours you don’t need that R-values applique as a cost driver. And according to my friend, who has researched this with due diligence and is a former contractor, he recommended that the inert gases are not necessarily needed either.
I’ve been looking into the same thing but I think I’m going to save a little money prior and go with a roof and go with another HVAC system but there are some things that can be done to retain heat or shed heat in the summer and one of those things is the underside of the roof in the attic. There’s this type of rolled and perforated wrap product that takes care of radiant heat and we applied that to a garage belonging to my contractor friends and it really made a big difference. His attic went from like a hundred and thirty degrees in the summer to around 90 to 100 degrees with the same product which doesn’t heat up the ductwork and is saving him both summertime energy costs and wintertime energy costs. That might be an Avenue you could explore rather than going right into the windows and expecting a magic cure all. Houses are in reality a system and all these subsystem components have to be in place in order to reap the savings that I think many imagine are going to be there with just new windows on.