IRule - combine 2 variables with an and && statment

The only thing I can see immediately is that you did not have $lower_uri defined. Here is iRule reformatted using "class match" rather than matchclass (which has been deprecated).

when CLIENT_ACCEPTED {

    set group "group_web_uri_dddMobile"
    set group_web_mobile_user_agents "group_web_mobile_user_agents"
}
when HTTP_REQUEST {

     Set the user-agent field to all lower case so that the data group matches are not case sensitive

    set user_agent [string tolower [HTTP::header User-Agent]] 
    set non_mobile_pool "www.ddd.com" 
    set mobile_url "http://m.ddd.com" 
    set redirect_to_mobile "false" 
    set group $::group_web_uri_dddMobile

     Determine if the user agent (all lower case) is a member of the data group 
    if { [class match $user_agent contains $group_web_mobile_user_agents] } { 
         log local0. "dddMobile - User-agent ($user_agent) is a member of the group_mobile_user-agents data group" 
        set redirect_to_mobile "true"
         Check to see if it is an Android tablet. If it is, do not send it to the mobile site
        if { ( $user_agent contains "android" ) && not ( $user_agent contains "mobile" ) } {
             log local0. "dddMobile - User-agent ($user_agent) contains Android but is not Mobile"  
            set redirect_to_mobile "false"
        }
    } else { 
         log local0. "dddMobile - User-agent ($user_agent) is NOT a member of the group_mobile_user-agents data group" 
        set redirect_to_mobile "false" 
    }

     Now send the request to the appropriate destination based upon the value of the redirect_to_mobile variable 
    if { ( $redirect_to_mobile == "true" && [class match [string tolower [HTTP::uri]] starts_with $group] } { 
        HTTP::redirect "$mobile_url[HTTP::uri]"
    } else { 
        pool $non_mobile_pool 
    }
}