Not too sure if BM would work well for mobiles as there is no roaming setup.
TG9 is linked between a few local repeaters in some areas (http://www.bm-dmr.uk/dashboard/BM%20UK.pdf
One would need to check if they are able to roam but then it's limited compared to the likes of the Phoenix roaming groups.
There's no harm in trying to get more repeaters even if it is a small coverage range.
There are a few locations where people and groups have setup for BM and Phoenix both on the same and different sites.
Leicester has both Phoenix and BM over two sites whereas Weston Super Mare has numerous repeaters on one site.
Baofeng UV-5R , Motorola DM4600 , Moonraker HT-500D , TYT MD-9600 , Ailunce HD1 , Anytone AT-D868UV , Retevis RT8 , DV Mega Bluestack (Pi-Star)
Local repeaters GB7CT , GB7WL , GB7HR , GB7NS , GB7GF and GB7BK
Admin : http://www.dmr-uk.net