It seems not a good return, 100 coins to make 0.2 coins per day... if you use those coins to buy miners, only 40 coins could make you 0.2 coins per day
But those 40 BTC are then gone, and may never see ROI let alone any profit. The 100BTC (if he's a holder anyway) are better working for him than sitting in some dumb safe wallet.
Not any bigger than the platform being "hacked"
Trying to invest in bitcoin and get more bitcoin back is quite old way of thinking, "investing" only applies to fiat money since fiat money lose value by itself thus you are forced to invest. For bitcoin hodling is the best investing method and almost risk free