问题
What would be the difference (if any) and advantages/disadvantages between these two properties used to determine the user agent?
Dim strUserAgt as String
userAgent = Request.userAgent
vs.
Dim strUserAgt as String = Request.ServerVariables("HTTP_USER_AGENT")
回答1:
Source: How to determine browser type in server-side code without the BrowserType object in ASP.NET
In ASP.NET, you can access the Request.ServerVariables collection or use the new Request.UserAgent property to retrieve the HTTP_USER_AGENT header value.
There are no difference, both will retrieve same thing HTTP_USER_AGENT header value.
Check Request.ServerVariables Collection and IIS Server Variables if you want to dig it in deep. These server variables collection values somewhat depend ond the IIS version also.
来源：https://stackoverflow.com/questions/11472820/httprequest-servervariables-vs-httprequest-useragent-properties-vb-net