The JP that belly landed didn't have live seats!! So the crew didnt have much of a choice and were very lucky!!IMHO
Live seats in the civvie market.....
The MOD do disarm the seats before sale.
However, there are companies who specialise in servicing and certifying e seats in the civvie market.
The CAA suggest that any swept wing, e seat equipped a/c should have live seats. IMHO any a/c that was equipped with an e seat should have a working e seat installed whoever owns it.
The north weald guy was very lucky to live and it was because of the preflight brief he had that he was able to pull the manual overide handle and loose the seat and deploy the chute although he wasnt "ejected". The seat was found to have a worn toplatch which allowed the seat to slide out and through the canopy when inverted (with passenger attatched) He didnt even have the harness leg loops on properly and was saved only by the release box jamming in his upper clothing and a wider chest than waist.
Civvy jets with bang seats info here