I also use 高速煲 to 炆牛腩. I put also carrots in it. I cook it for 35 mins. I think the 牛腩 is very nice and soft (no 爛溶溶) but the carrots are abit soft. I just put the mixture to cover the beef and carrots only. Maybe you put too much water?!
I also use it to cook soup, I think it's very good!