I bought this to stop allergens. I can't say I really like it for other reasons.
Pro: Peace of mind because it has a waterproof layer, means almost nothing goes through it.
Cons: Waterproof layer means it comes out of the washing machine sopping wet, even after turning it inside out and spinning it again. Takes more than an hour in the dryer, even with a dry bath towel added to help it dry faster. No tie tabs on the inside of the cover, and because of the slippery waterproof layer inside, the duvet floats around almost instantly. The waterproof layer means less air goes through it, so I toss and turn from overheating. Duvet off, duvet on, even though I'm a cold sleeper. This doesn't happen with a tight weave all-cotton protector. My husband complained about a bleach smell from the cover. It does smell quite strongly like new plastic and bleach, even after I washed it (without any bleach).
Overall, more cons than pros. The waterproof layer causes a lot more hassle. It's bad enough having to wash waterproof mattress covers, but add these as well, and your dryer will be running all day. I'm reluctant to add chemicals to kill dust mites in the wash, so using a dryer is a must for me. I don't think I'll be using these covers often. I'll go back to my all-cotton protectors. I can't return these now that they've been washed and used, so lesson learned. No more waterproof duvet covers.