The ego mega attys are just large 510 attys. The filler in the cartridge holds the juice. It is transferred to the coil via the bridge and wick. What you have is not a bridgeless dripping atty, but you might find that dripping a mega atty rather than using it as a standard atty/cartridge system is worthwhile.
The ego mega attys work well and are easy to clean. They produce a lot of vapor and the flavor holds up well. Frankly, I've always been surprised they didn't become more popular than they did, but since they were only around a couple of months before the ego-t attys (which is what you said you were really trying to buy) and the ego-t was widely hyped as the next best thing since sliced bread. The ego-t was probably the single most popular vaping product ever for the first half of 2011. I can't think of another device that got so much attention from the vendors and forum users...
The downside to the mega atty's is the fact that the white filler in the cartridges is hit and miss. They are easy to overfill - and they can tend to overfeed and flood. The blue fluval mod makes a big difference. Also, thicker juices tend not to overfeed as badly as thinner juices so you might have good luck with a high VG ratio juice.
Anyway, here's a video tutorial (he's using the totally wicked version, so he calls it a tornado instead of an ego-mega)