I see specific adavantages to very specific applications. i.e. remote workers, remote offices, small annexes of a campus where cabling costs are prohibitive. Other than that, I see no reason to spend the money. Especially now that Avaya has found 2 more RTU's they can now screw you for. First purchase station ports, then you can buy the IP Hardphone RTU's, then pay for Concurrent IP Sessions, then you'll have all the appropriate rights to spend more money and buy the actual medpro, c-lan's, and phones to get it to work. At the end of the day, there's nothing magical about it. It's just a phone on a desk.
-CL