Many clients wouldn't find this sufficient for user acceptance testing. Won't any mildly tech-saavy client want to try it on their laptop, phone and/or tablet

Many clients wouldn't find this sufficient for user acceptance testing. Won't any mildly tech-saavy client want to try it on their laptop, phone and/or tablet to make sure it looks right in different browsers? Well, it'll look exactly the same, because they aren't actually rendering it.... The minify/obfuscate solution seems sufficient (and possibly an expiration date...) but even that would be obviously unnecessary with many clients.