"First of all it was a miss in terms of profit – second in terms of cost cutting, if you compare to Rio Tinto, it is nowhere near Rio in terms of the amount of cost cutting they could do," portfolio manager at Sturgeon Capital, Yannick Naud told CNBC.
The planned demerger will leave BHP Billiton almost exclusively focused on four main "pillars" – long-life iron ore, copper, coal, petroleum – and potentially potash basins which will spur cash flow growth and boost returns, the group said.
"People are asking now, is this creating value for shareholders? You don't want a corporate transaction that you don't understand and don't quite know what you're getting out of it," said fund manager at 7 Investment Management Ben Kumar.
The new spin-off company, named NewCo, will be headquartered in Perth and listed on the Australian stock exchange with a second listing in South Africa. The business will combine aluminium, coal, manganese, nickel and silver assets and will be managed separately.
BHP Billiton shareholders will receive shares in the new company on a pro rata basis.
"We knew there would be a spin off; we knew that the focus of today would be capital return. I think the market is disappointed by the fact there is no announcement of share buy-back. But in terms of efficiency, in terms of being a lower cost producer, Rio Tinto is ticking all the boxes," he said.
Read MoreMiners upbeat despite the prevailing headwinds
U.K. fund manager Mike Felton said he has struggled to find value opportunities in the U.K. market this year but Rio Tinto has been among the fund's best performers this summer
"As a low-cost producer of iron ore, Rio is currently benefiting from robust prices," he said.
After the success of Rio, Felton recently added to his stake in BHP Billiton, as he sees the sector as attractive as firms continue to cut costs.
Gold miners have rallied 26 percent since the start of the year, with gold mining stocks trading at a 58 percent discount to 2011 levels according to ETF securities.
Historically, the third quarter has been a strong period of performance for gold miners given the seasonality of gold demand, the group said, who see now as a good time to raise exposure to the sector.
Read MorePaulson holds onto gold ETF, Soros adds gold miners
"We don't own base metal miners but we own gold miners," partner at RMG Wealth Management, Stewart Richardson said.
"Going back seven or eight years, the gold price has gone up relatively significantly despite the poor performance last year and yet gold miners have gone nowhere," he said.
"We know if the underlying profitability of the gold price comes down further, that will accelerate any further write offs and that will create a cleaning of the excess so to speak," he said.