I have had these Tala Measuring cups for a little over 4 years and now ordered another set. So I can speak for their durability, I find it best to remove the ring and only use this for storing the cups.
When I have finished with them I just put them through the dishwasher (putting the prongs through the holes and fitting the cover back over the top as they do have a tendency to flip over and fill up), they have never dis-coloured or gone brittle, so I would presume these are dishwasher safe.
The last set of these that I bought were 240ml/1cup =English Measures The 1st ones I have are American 237ml/1cup. I have learned there is no Difference to the outcome of the recipe if you use All English Measures on an American recipe remember Fluid measures are slightly different to dry measures (only slightly to check the accuricy of any cup or jug pop the on scales calibrate it fill with water to desired quantity and weigh out 240ml should weigh 240g, 15ml should weigh 15g)
Just make sure you use all English or all american cup measures and your cakes will turn out just fine. There are generally alot of eggs in american cakes so you don't need to add extra soda/baking soda (bicarb/ baking powder)as eggs are a raising agent.
I find my fingers better than the egg separator as sometimes the yolk slides through the vents bursting as it hits the bowl (especially small eggs) but other than that they are super.
I tend to use my fingers instead of the leveller too, the weights and measures on it come in handy especially when baking with the children, Which is why I have just bought another set. As they both like to measure the ingredients out together it'll save arguments.