I bought this mattress cover for my new mattress, which is a very cushy pillow top. When I tested the mattress in the store it felt very plush and I look forward to sleeping on it. Once it was delivered and I put the mattress cover on it there was a noticeable change in the feel of the mattress; it felt firmer than it had in the store.  So after a few nights of this I peeled off the mattress cover and stretched out on the mattress without it. At last!  The mattress I had anticipated. 
Long story short, if you have a very soft mattress this mattress cover may change the way your mattress feels. If you have a firmer mattress it may be fine. In all other respects I’m sure it’s an efficient barrier to bedbugs, allergens and dust as advertised.