I notice that all the stretch jersey on that website seems to be at least 350 gsm and some of it is over 500 and still recommended for tops and baby clothes. I recently made a warm jacket from some really thick sweatshirt fleece said to be 280 gsm. You'd wonder do they make these figures up!
On that basis I'd be inclined to order a sample and I'd be very interested to know what your verdict is.