My Escapac IG3 certainly hurt when it went off...and that was only just a little bit less than when the ballistic spreader fired. The seat was an original Zero/Zero seat and it had many problems due to its antiquity. In my view, the rate of acceleration from the rocket coupled to the instant deceleration from the ballistic spreader was close to a fatal mix in any circumstance.
Having flown both types, given the choice of cockpit in an "A4 vs SHAR knife fight" I would choose the SHAR every time. Even with the FRS1, the radar and air to air weapons aiming system was superior in all respects. And the thrust advantage with the Sea Jet was enough to counteract any turn rate advantage the lower wing-loaded A4 might have felt.
NB: I never flew an A4M, but am fairly sure they didn't have a radar. Entering a fight without a radar is like being blind in a room full of enemies who can see.