I've been using the Metro Expresslanes at least 4 times a month so I don't get charged the monthly maintenance fee, and like others I did not want to put the sticky strips on my window for the Fastrak, so I bought this instead: Amazon.com: JL Safety NEW Indestructible holder that fits the NEW 2012 and OLD EZ Pass, I Pass, I Zoom, PalPass hard case and FasTrak transponders. Slip Fit, Will NOT Rotate or Rattle. Unlike plastic, this one will not Melt, Warp, break or Discolor. The Only Metal Holder Available Designed Not to Interfere with signal Reception. Very Easy to Attach and Remove, No Messy Adhesive. Holder only, transponder not included. US Patent and Lifetime Warranty. Made in USA.: Industrial & Scientific It works great to hold the transponder on the window. I was afraid of just leaving it on the dash and running the risk of a cop giving me a ticket for not fixing it to the window, so I assume this should work for that (but don't quote me on it). For less than $10 I would recommend it to anyone who does not want to permanently attach their Fastrak transponder to their cars.
In addition, I noticed on their website that they are imposing a mandatory $1 fee for a "monthly maintenance" fee, whatever that means, fyi for people who have an account.