Based on my experience with Onset's HOBOlink service, I would caution to add that you also have no idea how timely weatherlink.com's servers will (or won't) be in pushing your data along to WU. It may not be immediate, or it could be held for a batch-send, or simply given lower priority to other server tasks.
With HOBOlink, this all happens "behind the curtain" and the user has no way of knowing unless he or she tries to do some detective work. I can say from careful observation of my very long update lags, that on WU the update time shown on the PWS page has changed. I could tell that it used to reflect the time the data push was received by WU, and now it shows the observation timestamp of the data instead. Perhaps someone here has carefully observed the weatherlink.com data against the console data to determine if there is any latency.
Rich K.