I'm curious to see how this works. The 100-page Giant formats were great for DC in the 1970s.
Back before LCS proliferated through even modestly sized towns. Back before digital distribution.
Those giants were likely the first exposure to a lot of DC's properties and heritage. They certainly were for me (I still remember marveling at the discovery that the JL had once included a bald green dude). But even the original experiment in these formats didn't last all that long if I remember correctly.
I'd expect some initial enthusiasm, followed by a tapering off for these comics. I guess the hope is that the reprints will stimulate fans to seek out runs of the older material, be that in hardcopy collections or through DCUniverse subscriptions. As a tool to inspire increased purchase of their monthly content? I'm not so sure; at least, not as a long-term strategy.