When valuing non .com domains, I like to see how the domain looks in the .com form.
If the domain is not functional or has no established website in the .com form, that's a good indication that other forms of the domain like .net, .org. .us, are of no real value.
If the domain has a functioning website in the .com form, the website looks good, the website is owned by a company, and that domain is popular, there's a good possibility that other companies/individuals in that same industry may have been interested in buying that domain - but were unable to get it. Only one buyer can purchase the domain name.
In this case, masking.com is forwarded to another website for Polytak protection systems. Polytak is a national supplier of temporary adhesive films to the construction, recreational vehicle, building, marine, and retail markets.
It seems logical to me that there may be other companies in the same industry that may think that the word "masking" is valuable and important.
If consumers and domain end users get used to the .us extension and .us catches on, then I would not be surprised if you received an offer from a company in the same industry as Polytak protection systems within the next 2-3 years.