K Rend vs conventional cement render

Hello folks

I’m trying to decide whether to go K Rend or conventional render on a new extension we’re having built- single storey 7x5m lots of glass and doors. I’m veering away from K-Rend at the moment but our builder is saying it will cost an extra £2k to go conventional render. Is he blowing smoke up the proverbial?

Cheers
Jez