As Andy mentioned, this is a tricky question. Are you looking to patent the product? Or the process of making the product?
Forgive me if I point out the obvious to you. Patenting a product is certainly possible, but you have to document how your product is different in form/function – and this is finicky enough that you would be best to engage a patent attorney to write the provisional patent and file it. The process takes quite a long time through to granted patent – minimum 18 months in NZ.
A consideration is that if you do indeed gain a granted patent for a differentiated product in a crowded category, that shows that others could do the same.
Process patents, focusing on HOW something is made can be more powerful in ‘blocking’ others, but you have to ‘reduced it practice’ – that is you have to make it and show data on that process.
It may be easier to trademark the shape of the product, which gives you some protection and is cheaper and easier to obtain. Again, you are best served to engage a patent attorney for this work to get it right.
Agree with Andy’s comments re: manufacturers.