Really? What LOC rate do you have? Most LOC rates are about 9.49% pa range, whilst margin loans are slightly higher starting from around 10%. In most cases, LOCs are lower than MLs in terms of rates, which is an advantage of LOCs. Also, no chance of being margin called if your investment / loan breaches the buffer.
LOCs are still tax deductible as long as the investment you invest in is deemed to be "income generating" asset.
A disadvantage of the LOC is you will generally have to mortgage your property as security, so if the investment tanks and you default on the loan, they might take your home/investment property.
Either way, it's still gearing. Usually double edged sword benefit/costs of gearing.