Peacocks are large -- up to about seven inches -- and are very inefficient eaters. Nutrient export (and thus algae, diatoms, slime, high nitrates, etc) is a problem with these guys. I run a 30 with a 10 gallon reverse-light-cycle refugium and chaeto, a good skimmer (Remora), PolyFilter and PhosGuard, and feed every other day -- and I still have a run-away algae problem. Note that "standard" cleanup crews are going to get eaten. Non-standard cleanup crews, including urchins, are hit/miss. My peacock tolerated a tuxedo urchin for months before chowing down. I am trying lettuce sea slugs next.
Depending on the individual and the sex, peacocks roam around quite a bit (males more so than females). While a peacock may "survive" in a 10, well, humans can survive indefinitely in jail cells. It's an over-used but IMO reasonable analogy. If you want to keep your critter happy, give it more room.
I think for it's size, the "smaller" spearer P. ciliata requires the most room "ideally" than any other mantis. It really needs a 20, yet gets only like 4" long.
As for the acrylic, yes, it's about the glass. A larger peacock is *able* to break thinner glass. They often will do this when burrowing. You can get away with putting a layer of acrylic on the bottom of a glass tank, and avoid really thin tanks. I'd try for 1/4" (5-6mm) glass, if you want a glass tank.
Dan