How prevalent are anti-explosion bladders in fuel tanks?
According to this wikipedia article :

Most jet fighters and all US military rotary wing aircraft have some type of self-sealing tanks. Military rotary wing fuel tanks have the
additional feature of being crashworthy. High altitudes require the
tanks to be pressurized, making self-sealing difficult. Newer
technologies have brought advances like inert foam-filled tanks to
prevent detonation. This foam is an open cell foam that effectively
divides the gas space above the remaining fuel into thousands of small
spaces, none of which contain sufficient vapour to support combustion.
This foam also serves to reduce fuel slosh. Major manufacturers of
this technology include Hutchinson, Amfuel (Zodiac) (formerly
Firestone), Meggitt (formerly Goodyear), Robertson Fuel Systems, GKN
USA and FPT Industries. FPT is now part of GKN. For military use,
tanks are qualified to MIL-DTL-27422 (includes crashworthiness
requirements) or MIL-DTL-5578 (non-crashworthy). An aircraft fuel tank
sometimes consists of several interconnected fuel cells. The
interconnecting hoses are typically also self-sealing.
In addition to fighter aircraft some military patrol vehicles and
armoured VIP limousines feature self-sealing fuel tanks.
Self-sealing fuel tanks using military technology are also required in some motorsport categories.

Given the fact anti explosion tanks were invented in 1917, and are in use since then, and have undergone many technological advances since then, they are being used quite commonly and in most of the planes where pressurization is required.