If you are working in areas classified as hazardous areas under a code such as BS60079 then as you will know equipment brought regularly into those areas must be ATEX certified, and these items are not. You might be allowed by carrying a portable gas detector under a work permit on an occasional basis, but that's the area authority call and your employer can't oblige them to let you do so. If the sites don't have hazardous areas, then you might be able to negotiate, but it all depends on how likely you are to stray into hazardous areas inadvertently.
The libre is different, it has low voltage and so low risk potential, same reason you can now wear digital watches (but not smart watches) on site.
Your best bet is to ask your employer if they'd consider buying you an ATEX rated mobile for work, they exist and would solve this issue. On the plus side if you are surveying it gives you the ability to take photos without needing a work permit for bringing a camera on site.
Edit: didn't realise this was an old thread.