I have been told before that budgies don't need grit but does that include oyster shell grit. Can I give them this or is this also unnecessary for them.. if it's OK should I mix it with food or in a separate dish.thank you.
Oyster grit is a calcium source often fed when breeding. It is a good source of minerals, not to be confused with insoluble grit which is more for birds that need to grind their food.
However, you can provide plenty of calcium for most budgies by simply providing a cuttle fish bone. This is a safer option as you may get the occasional (though rare) bird that scoffs the grit and causes themselves harm. This is more likely with the insoluble grit which doesn't easily break down in the crop and can cause blockages. I suspect this is more likely in a pet situation where there is less to keep them stimulated than in an aviary flock setting.
So, go for cuttle fish if you think they need more calcium, especially if they are not breeding, as they require only a fraction of the calcium that a breeding bird does.