I'm not sure what the question is. When you trigger an SOS, your coordinates are sent to GEOS. GEOS will pass them on local SAR if a response is required. Not that it matters, but I would assume that the coordinates are actually transmitted in WGS 84, since that's the standard datum for GPS devices.
Neither GEOS nor the local SAR organizations are limited to the datums available on the Mini itself. They'll be equipped to convert from one datum to another. (Any GPS unit can do this, assuming only that both the from and the to datums are available on the unit.) And if the SAR organization chooses to operate on the OS grid, I'm sure they can do so.
good info from twolpert - cheers. your educated guess about 66 line is correct. just to be thorough i phoned garmin gb again just now and confirmed that neither the explorer nor the se can display os gridrefs. they recommend the 66i. currently an eyewatering and i would think 'for professionals only' price of £549.99.
point being i guess, 4392091 (and just to restate twolpert's knowledgeable post) is that for an sos call it doesn't matter as far as your rescuers are concerned - they will find you with wgs84 coordinates. but if you want to relate handset info to and from an os map then you will need a device other than the inreach mini, explorer or se.
this should be made FAR FAR clearer in uk marketing.
The only iR device which supports this is the 66i and the related 86i. If you are using any other inReach device, the answer is no.
You can open a support ticket to confirm and inquire about future features. But I doubt that the feature will be retrofitted into any of the legacy devices (SE+/Explorer+) or the transitional Mini. These devices are not full members of the Garmin ecosystem and are not receiving major enhancements as far as I know.
