The UK Flight Training web-site features all the aircraft that can be found at Rainbow Air, also at Long Beach. So, I don't know if they have merged or have a partnership.
I have flown with Rainbow Air and can vouch that they are are good, reputable establishment with good aircraft, and their own maintenance facility. When I was there last, a number of UK guys were doing their FAA PPL, and were happy with the place.
If you can fly in LA's airspace you can fly anywhere in the world - the airspace is unbelievable - your RT standard would be far higher than anywhere in the UK.