You don't need to buy an MTB shoe for the eggbeaters. As long as the shoe has a 2 hole for the cleats, you can use that shoe. Shimano's shoes has the 2-hole and 3-hole triangle for the cleats. Crankbrothers also has an adapter for a 3-hole if your shoe does not have a 2-hole.

http://crankbrothers.com/accessories_cleats.php

One advantage of the eggbeaters is you can easily clip out. Another is the minimalist and gorgeous design - imho.

However, I really found it hard to clip in (maybe because I was using a road shoe or got used to a SPD-SL cleats). You also actually lose a lot of power transfer compared to a SPD-SL since your shoe tends to sway from side-to-side when your pedaling especially on an uphill where you tend to stand up. Lastly, compared to Shimano 105 clipless pedal, your shoe clearance to your bike's frame when clipped-in is shorter. Many times, I had my shoe hit the lower part of my bike frame.

These factors made me decide to go back using my 105 clipless pedal. Goodluck!