Simply put, the quantitative comfort of the economy, in the absence of OMT, does not really help to prevent investors from benefiting from QE by lending to banks in return for collateral to cover the transaction costs. You may not realize that, according to current accounting and MTL standards, a single Euro add-on interest payment is already enough to earn risk-free profit for the majority of banks, so that what might be considered shedding hands to speculate once every few years, is not really unique and is replicated
The next most common type of interest-bearing instruments is bonds. Bonds are basically pooling deposits into a fixed return that must be invested or paid back or borrowed. Bonds are variable, so they can earn interest a variable amount of times, in rates that vary from 1% to 20%. Bonds were usually available only to investors who owned specific types of asset without worrying about additional returns options and could thus economy.