My husband and I are laying a tongue and groove engineered wood floor. As of now, we're going to use a moisture and sound barrier underlayment in one. There is the cheaper option at about $10/ roll: Unison 2 in 1 foam underlayment. Then there's the more expensive one's priced $40 and up. The area we're doing is about 750 sq ft. Some of the flooring will be layed on concrete slab and some on wood subfloor. Are the pricier underlayments worth it? What sort of characteristics should I be looking for in an underlayment? We've spent over $3000 on the flooring, so I want to protect our investment. Any suggestions would be greatly appreciated.