As OTAHD mentioned, the URC remotes have an extremely powerful IR blaster on the remote unit itself.
I even tried placing a folded towel in front of the IR window, and it still transmitted signals with no problem!
Masking the IR window would not be practical, unless you want to tape a small pillow to the front of the unit.
The MX-350, although the runt of the litter (the lowest in the Professional line) is the sleeper of the bunch.
Don't let it fool you, it's much more flexible than the MX-600 and MX-500, and has some of URC's newer features in it.
It is a full functioned, very powerful remote, and hard to beat for the money.
Should your system grow or your needs change, you can add an RF base station later, something you can't do with an MX-500.
If you have the need for constant upgrading of the device database, URC now makes the PCL-300 which allows you to update the database and save your programming by software into a laptop or home computer.
It is IR/RF switchable, and addressable, making it compatible with the MRF-200, 250, 300, and even 350 (without the narrow band RF feature).