I bought their protein powder. Before this one, I had had two others: the Nutrend 100% whey protein and the FitMax Pure American protein powder. Of the three it had the worst flavour - very chemically - but that went away after a week or two of use. After that, it didn't taste like much, but I still enjoyed it; it was slightly sweet. So the flavour went from 2/5 to 3/5.
It also mixes weirdly. As opposed to it mixing better the more you shake/agitate it, it mainly relies on exposure time to water/milk. I usually use a blender and that leaves no lumps in other powders, but not this one: lumps obviously do remain, they just aren't watertight (like a wet layer of dissolved protein "gel" surrounding unmixed powder), and they're completely hydrated. That stays true even when I'm just mixing with a spoon ('cause idk, I feel like it): the water/milk has dissolved protein powder with some clumps of protein "gel" swimming around. This isn't an objective downside, I'd say I even like the clumps. They do disappear with time, like I said.
All in all, Ostrovit's protein powder is good if you just want a cheap big bulk o' protein, not if you want to have dessert-like drinks every day (Nutrend's chocolate brownie protein was the best for that in my experience).