Just because you have to display metric currently doesn't mean it's consistent metric units. If they want to take the comparison point from the consumer they already are.
I buy a jar of something, one brand is priced per ml and one is priced per 100g. I don't know the density of 'thing' so I don't know which is better value.
I buy a packet of something, one brand priced per 100g and one per each. Same issue. Also with fresh fruit/veg.
I go to the market I have to choose whether to buy per lb or per bowl, with no idea which is better value because I don't know what a lb of apples looks like.
And that's assuming that the mg-g-kg etc conversions are trivial which they aren't for everyone.
And there's a total lack of clarity whether the price per refers to the normal price of the discount price (when there is one).
I don't really care if it's metric or imperial or something else. What would help the consumer is consistency across a product type within the same shop, which isn't available now and what metric was supposed to do.
And metric isn't the scientific standard it's made out to be. Metric is standard in science in most western countries. The rest of the world tends to go with some sort of mix up like the US and UK. Scientists are generally not going to bother with unit conversions if it can be avoided and will use whatever the data is provided in with little consistency across company/industry. And that's on top of inconsistently recording either the volume or weight or moles or whatever. Telling scientists, here are some sensible SI units and you should use them, didn't actually change anything, equipment is expensive and conversions imprecise and nobody thought to record whether things were metric or imperial.