The SMEs have a very limited remit - they have to confirm that the claims made by the contractor about the aircraft's performance and equipment are backed up with appropriate factual documentation (the RFM generally) and that said factual information is included in the bid.
I think there is only one aircraft type actually in the running as it has already proved itself at 2 MCA flts (and I'm not talking about the 139
) and all the bidders have offered it.
At the point where we have to concern ourselves where the casualty is and who will pay before rescuing him will be the point at which UKSAR ceases to be the world-leading organisation it has been for so many years and the point where all the concerns about privatising SAR come true - let us hope it never gets to that!