It's definitely memorable, the problem is it's almost too generic to the point where the keyword doesn't have any obvious commercial use. For example, if you put product into a Google search, you get no sponsored links. Sponsored link adverisers are potential buyers for your domain, without them, it's difficult to get more than reseller value.
I agree about the Pro Pro thing. I registered Projector.pro for that reason. I think it could work for a product ratings site, you just need to find the end user. I regged Feedback.pro for a product ratings, survey, or market research site.
As a general commercial site, it could work, but there are plenty of unregistered keywords available with the .pro extension. I registered Buyer.pro last week and that's got the angle of referring to a profession on top of the buying something thing.
Value wise, I'd say small multiple of reg if you find the right reseller because it is memorable, difficult to second guess end user value because end users aren't using .pro yet and probably haven't even heard of it. When they do start developing .pro's I doubt they will get to Product.pro quickly but you never know.
The problem with asking for appraisals on newly regged .pros is realistically, if anybody at this point genuinely considered it was worth more than $100, they would have registered it themselves.