I've lived in Malaysia for 12 years.
DHs job brought us here originally but I am now a Governor at my DDs' school and I teach ESL and English Lit at another smaller school.
Epsom is still a newly established school (been running 3ish years)
I've heard good things about the senior school but heard there were issues around the prep school, the head was unpopular (with staff and parents) but has now gone but there have been some ongoing staffing issues.
It is still not full apparently and feels a bit "empty".
It's a long school day 8.15-6pm (but I think this is normal for boarding)
It's near Sepang, so it is a good way out of KL centre and transport links are minimal, so you would have to drive to social events, or live further away and commute to school. (As it's a boarding school, you might have to live on site, this would mean your entire social life is based around the school- and you are a long way from anything else, except the F1 circuit)
There are a lot of international schools in KL recruiting - also look at ALice Smith, Garden International, Desa Park City School, British School of Kuala Lumpur. All good, reputable schools. All competing for well qualified experienced UK staff for next academic year.
Living in Malaysia is fine, when job seeking, check if you will be paid in £, $ or RM (the exchange rate is not good atm), you need medical, housing, and education for all your dc as a minimum.
Regarding whether it would be "too different", that would depend entirely on your approach. You can very easily live in an expat bubble or embrace the culture completely. Most people do something inbetween.
My DC go to one of the major expat schools and most of my good friends are also expat (though not all British by any means), my local experience comes from work - I am at a much smaller "international" school, which is totally aimed at the local market (the state system is not fit for purpose) and I'm the only expat on the staff. You know you're in proper Malaysia when you are no longer surprised that someone has left you a bag of dried fish on your desk.
Kuala Lumpur itself is not that interesting a place after a while, but it's a great base to travel from - Singapore, Bali, Thailand, Vietnam all accessible easily.