1) Can't do brown out or white out landings without a lot of fancy kit and training.
2) Crap for low-level, mountain work
3) Not particularly manoeuvrable, not great range
4) Wrong speed for escort helis or fighter cover
5) Clumsy radar and noise signature
5) Hopeless for fast-roping due to massive downwash
6) Can it drop HALO ore even static line? Dunno but if it can probably not good at it.
7) Can't autorotate, can't glide
8) Heavy maintenance support
Great maybe for niche role for US special ops with no budget limit - but too specialist for UKSF budget and ethos.